Fix #5012: Remove KitKat support

[BenHenning]

Explanation

Fixes #5012

Removes references and code corresponding to KitKat (SDK version 19) since the app has been set to a minimum version of Lollipop (SDK 21) since #3910 (roughly--technically KitKat was still supported but we no longer shipped a KitKat version). Because of this, the changes in this PR are largely a no-op from a build perspective.

More broadly, this change is motivated by a desire to decrease CI time (which was already reduce considerably in the recent merge of #5629) by removing extraneous app builds being done in CI:

• //:oppia since we should really only use //:oppia_dev moving forward.
• Dev and alpha KitKat builds (the latter of which takes a long time since only the alpha job was building 2 proguarded builds of the app and thus taking much more time than the beta and GA build jobs).

Separately, build_tests.yml and unit_tests.yml were updated to no longer support caching since we disabled this behavior a while back (#2884) and are unlikely to reintroduce it due to high storage costs.

Some other noteworthy changes:

• The optional providing of Retrofit and Retrofit services has been reverted since it's no longer necessary (and corresponding tests have been removed since there's no longer any condition to verify).
• Code that was gated to run below Lollipop has been removed since it can't execute except on KitKat devices.
• Support for a main dex target list has been removed as we're unlikely to need it with native multidex support (which wasn't an option for KitKat builds), though we may choose to reintroduce it to speed up cold app starts since it can potentially help improve time-to-splash app startup performance.
• Updated manifest min SDK values to avoid potential developer confusion on the min SDK version supported (though, strictly speaking, this doesn't technically matter with the way the app builds).
• This updates the default min version supported for OS deprecation. No additional work is needed to actually activate the deprecation notice on the KitKat version of the app since we no longer deploy it, and OS deprecation wasn't added to the last version that was deployed.
• Three file content pattern failure messages were updated to no longer reference KitKat (though the value of these checks mostly still seems realized, so I think it's fine to keep them in).
• Some additional licenses were added due to tooling around the dev AAB (even though these aren't dependencies that ship with the app). I think it's fine including extra licenses in this case.
• The protobuf license was corrected to BSD 3-Clause as declared for the dependency and in the GitHub repository for the dependencies.
• This bumps version codes due to removing two flavors (for KitKat dev and KitKat alpha).

Note that there are some workflow job removals and renames in this PR. Any required CI checks will be correspondingly updated once this PR is approved and ready to merge (to avoid blocking any other in-flight PRs).

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

This shouldn't have an side effects on non-KitKat UIs, and KitKat support itself is being removed in this PR (so there's nothing to demonstrate).

[BenHenning]

Self-reviewed.

[github-actions]

APK & AAB differences analysis

Note that this is a summarized snapshot. See the CI artifacts for detailed differences.

Dev

Expand to see flavor specifics

Universal APK

APK file size: 19 MiB (old), 19 MiB (new), 1768 bytes (Removed)

APK download size (estimated): 17 MiB (old), 17 MiB (new), 2051 bytes (Removed)

Method count: 260202 (old), 260177 (new), 25 (Removed)

Features: 2 (old), 2 (new), 0 (No change)

Permissions: 6 (old), 6 (new), 0 (No change)

Resources: 6818 (old), 6818 (new), 0 (No change)

• Anim: 43 (old), 43 (new), 0 (No change)
• Animator: 26 (old), 26 (new), 0 (No change)
• Array: 15 (old), 15 (new), 0 (No change)
• Attr: 922 (old), 922 (new), 0 (No change)
• Bool: 9 (old), 9 (new), 0 (No change)
• Color: 967 (old), 967 (new), 0 (No change)
• Dimen: 1048 (old), 1048 (new), 0 (No change)
• Drawable: 380 (old), 380 (new), 0 (No change)
• Id: 1275 (old), 1275 (new), 0 (No change)
• Integer: 37 (old), 37 (new), 0 (No change)
• Interpolator: 11 (old), 11 (new), 0 (No change)
• Layout: 380 (old), 380 (new), 0 (No change)
• Menu: 3 (old), 3 (new), 0 (No change)
• Mipmap: 1 (old), 1 (new), 0 (No change)
• Plurals: 10 (old), 10 (new), 0 (No change)
• Raw: 2 (old), 2 (new), 0 (No change)
• String: 852 (old), 852 (new), 0 (No change)
• Style: 831 (old), 831 (new), 0 (No change)
• Xml: 6 (old), 6 (new), 0 (No change)

Lesson assets: 111 (old), 111 (new), 0 (No change)

AAB differences

Expand to see AAB specifics

Supported configurations:

• hdpi (same)
• ldpi (same)
• mdpi (same)
• tvdpi (same)
• xhdpi (same)
• xxhdpi (same)
• xxxhdpi (same)

Base APK

APK file size: 18 MiB (old), 18 MiB (new), 1764 bytes (Removed)
APK download size (estimated): 17 MiB (old), 17 MiB (new), 1223 bytes (Removed)
Method count: 260202 (old), 260177 (new), 25 (Removed)

Configuration hdpi

APK file size: 50 KiB (old), 50 KiB (new), 0 bytes (No change)
APK download size (estimated): 18 KiB (old), 18 KiB (new), 1 bytes (Added)

Configuration ldpi

APK file size: 49 KiB (old), 49 KiB (new), 0 bytes (No change)
APK download size (estimated): 14 KiB (old), 14 KiB (new), 0 bytes (No change)

Configuration mdpi

APK file size: 45 KiB (old), 45 KiB (new), 0 bytes (No change)
APK download size (estimated): 14 KiB (old), 14 KiB (new), 1 bytes (Added)

Configuration tvdpi

APK file size: 86 KiB (old), 86 KiB (new), 0 bytes (No change)
APK download size (estimated): 29 KiB (old), 29 KiB (new), 0 bytes (No change)

Configuration xhdpi

APK file size: 57 KiB (old), 57 KiB (new), 0 bytes (No change)
APK download size (estimated): 21 KiB (old), 21 KiB (new), 2 bytes (Added)

Configuration xxhdpi

APK file size: 63 KiB (old), 63 KiB (new), 0 bytes (No change)
APK download size (estimated): 29 KiB (old), 29 KiB (new), 2 bytes (Added)

Configuration xxxhdpi

APK file size: 63 KiB (old), 63 KiB (new), 0 bytes (No change)
APK download size (estimated): 28 KiB (old), 28 KiB (new), 0 bytes (No change)

Alpha

Expand to see flavor specifics

Universal APK

APK file size: 11 MiB (old), 11 MiB (new), 324 bytes (Removed)

APK download size (estimated): 10 MiB (old), 10 MiB (new), 886 bytes (Added)

Method count: 116281 (old), 116242 (new), 39 (Removed)

Features: 2 (old), 2 (new), 0 (No change)

Permissions: 6 (old), 6 (new), 0 (No change)

Resources: 5786 (old), 5786 (new), 0 (No change)

• Anim: 33 (old), 33 (new), 0 (No change)
• Animator: 24 (old), 24 (new), 0 (No change)
• Array: 14 (old), 14 (new), 0 (No change)
• Attr: 888 (old), 888 (new), 0 (No change)
• Bool: 8 (old), 8 (new), 0 (No change)
• Color: 820 (old), 820 (new), 0 (No change)
• Dimen: 780 (old), 780 (new), 0 (No change)
• Drawable: 342 (old), 342 (new), 0 (No change)
• Id: 1221 (old), 1221 (new), 0 (No change)
• Integer: 32 (old), 32 (new), 0 (No change)
• Interpolator: 11 (old), 11 (new), 0 (No change)
• Layout: 343 (old), 343 (new), 0 (No change)
• Menu: 1 (old), 1 (new), 0 (No change)
• Mipmap: 1 (old), 1 (new), 0 (No change)
• Plurals: 10 (old), 10 (new), 0 (No change)
• String: 785 (old), 785 (new), 0 (No change)
• Style: 472 (old), 472 (new), 0 (No change)
• Xml: 1 (old), 1 (new), 0 (No change)

Lesson assets: 111 (old), 111 (new), 0 (No change)

AAB differences

Expand to see AAB specifics

Supported configurations:

• hdpi (same)
• ldpi (same)
• mdpi (same)
• tvdpi (same)
• xhdpi (same)
• xxhdpi (same)
• xxxhdpi (same)

Base APK

APK file size: 11 MiB (old), 11 MiB (new), 324 bytes (Removed)
APK download size (estimated): 10 MiB (old), 10 MiB (new), 1002 bytes (Added)
Method count: 116281 (old), 116242 (new), 39 (Removed)

Configuration hdpi

APK file size: 43 KiB (old), 43 KiB (new), 0 bytes (No change)
APK download size (estimated): 17 KiB (old), 17 KiB (new), 1 bytes (Removed)

Configuration ldpi

APK file size: 44 KiB (old), 44 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 1 bytes (Added)

Configuration mdpi

APK file size: 38 KiB (old), 38 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 0 bytes (No change)

Configuration tvdpi

APK file size: 73 KiB (old), 73 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 0 bytes (No change)

Configuration xhdpi

APK file size: 50 KiB (old), 50 KiB (new), 0 bytes (No change)
APK download size (estimated): 20 KiB (old), 20 KiB (new), 1 bytes (Removed)

Configuration xxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 28 KiB (old), 28 KiB (new), 2 bytes (Added)

Configuration xxxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 0 bytes (No change)

Beta

Expand to see flavor specifics

Universal APK

APK file size: 11 MiB (old), 11 MiB (new), 108 bytes (Removed)

APK download size (estimated): 10 MiB (old), 10 MiB (new), 1105 bytes (Added)

Method count: 116287 (old), 116248 (new), 39 (Removed)

Features: 2 (old), 2 (new), 0 (No change)

Permissions: 6 (old), 6 (new), 0 (No change)

Resources: 5786 (old), 5786 (new), 0 (No change)

• Anim: 33 (old), 33 (new), 0 (No change)
• Animator: 24 (old), 24 (new), 0 (No change)
• Array: 14 (old), 14 (new), 0 (No change)
• Attr: 888 (old), 888 (new), 0 (No change)
• Bool: 8 (old), 8 (new), 0 (No change)
• Color: 820 (old), 820 (new), 0 (No change)
• Dimen: 780 (old), 780 (new), 0 (No change)
• Drawable: 342 (old), 342 (new), 0 (No change)
• Id: 1221 (old), 1221 (new), 0 (No change)
• Integer: 32 (old), 32 (new), 0 (No change)
• Interpolator: 11 (old), 11 (new), 0 (No change)
• Layout: 343 (old), 343 (new), 0 (No change)
• Menu: 1 (old), 1 (new), 0 (No change)
• Mipmap: 1 (old), 1 (new), 0 (No change)
• Plurals: 10 (old), 10 (new), 0 (No change)
• String: 785 (old), 785 (new), 0 (No change)
• Style: 472 (old), 472 (new), 0 (No change)
• Xml: 1 (old), 1 (new), 0 (No change)

Lesson assets: 111 (old), 111 (new), 0 (No change)

AAB differences

Expand to see AAB specifics

Supported configurations:

• hdpi (same)
• ldpi (same)
• mdpi (same)
• tvdpi (same)
• xhdpi (same)
• xxhdpi (same)
• xxxhdpi (same)

Base APK

APK file size: 11 MiB (old), 11 MiB (new), 108 bytes (Removed)
APK download size (estimated): 10 MiB (old), 10 MiB (new), 742 bytes (Added)
Method count: 116287 (old), 116248 (new), 39 (Removed)

Configuration hdpi

APK file size: 43 KiB (old), 43 KiB (new), 0 bytes (No change)
APK download size (estimated): 17 KiB (old), 17 KiB (new), 1 bytes (Added)

Configuration ldpi

APK file size: 44 KiB (old), 44 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 1 bytes (Added)

Configuration mdpi

APK file size: 38 KiB (old), 38 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 0 bytes (No change)

Configuration tvdpi

APK file size: 73 KiB (old), 73 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 3 bytes (Removed)

Configuration xhdpi

APK file size: 50 KiB (old), 50 KiB (new), 0 bytes (No change)
APK download size (estimated): 20 KiB (old), 20 KiB (new), 1 bytes (Added)

Configuration xxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 28 KiB (old), 28 KiB (new), 0 bytes (No change)

Configuration xxxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 0 bytes (No change)

Ga

Expand to see flavor specifics

Universal APK

APK file size: 11 MiB (old), 11 MiB (new), 32 bytes (Removed)

APK download size (estimated): 10 MiB (old), 10 MiB (new), 2603 bytes (Added)

Method count: 116287 (old), 116248 (new), 39 (Removed)

Features: 2 (old), 2 (new), 0 (No change)

Permissions: 6 (old), 6 (new), 0 (No change)

Resources: 5786 (old), 5786 (new), 0 (No change)

• Anim: 33 (old), 33 (new), 0 (No change)
• Animator: 24 (old), 24 (new), 0 (No change)
• Array: 14 (old), 14 (new), 0 (No change)
• Attr: 888 (old), 888 (new), 0 (No change)
• Bool: 8 (old), 8 (new), 0 (No change)
• Color: 820 (old), 820 (new), 0 (No change)
• Dimen: 780 (old), 780 (new), 0 (No change)
• Drawable: 342 (old), 342 (new), 0 (No change)
• Id: 1221 (old), 1221 (new), 0 (No change)
• Integer: 32 (old), 32 (new), 0 (No change)
• Interpolator: 11 (old), 11 (new), 0 (No change)
• Layout: 343 (old), 343 (new), 0 (No change)
• Menu: 1 (old), 1 (new), 0 (No change)
• Mipmap: 1 (old), 1 (new), 0 (No change)
• Plurals: 10 (old), 10 (new), 0 (No change)
• String: 785 (old), 785 (new), 0 (No change)
• Style: 472 (old), 472 (new), 0 (No change)
• Xml: 1 (old), 1 (new), 0 (No change)

Lesson assets: 111 (old), 111 (new), 0 (No change)

AAB differences

Expand to see AAB specifics

Supported configurations:

• hdpi (same)
• ldpi (same)
• mdpi (same)
• tvdpi (same)
• xhdpi (same)
• xxhdpi (same)
• xxxhdpi (same)

Base APK

APK file size: 11 MiB (old), 11 MiB (new), 36 bytes (Removed)
APK download size (estimated): 10 MiB (old), 10 MiB (new), 997 bytes (Added)
Method count: 116287 (old), 116248 (new), 39 (Removed)

Configuration hdpi

APK file size: 43 KiB (old), 43 KiB (new), 0 bytes (No change)
APK download size (estimated): 17 KiB (old), 17 KiB (new), 0 bytes (No change)

Configuration ldpi

APK file size: 44 KiB (old), 44 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 0 bytes (No change)

Configuration mdpi

APK file size: 38 KiB (old), 38 KiB (new), 0 bytes (No change)
APK download size (estimated): 13 KiB (old), 13 KiB (new), 0 bytes (No change)

Configuration tvdpi

APK file size: 73 KiB (old), 73 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 0 bytes (No change)

Configuration xhdpi

APK file size: 50 KiB (old), 50 KiB (new), 0 bytes (No change)
APK download size (estimated): 20 KiB (old), 20 KiB (new), 0 bytes (No change)

Configuration xxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 28 KiB (old), 28 KiB (new), 1 bytes (Added)

Configuration xxxhdpi

APK file size: 55 KiB (old), 55 KiB (new), 0 bytes (No change)
APK download size (estimated): 27 KiB (old), 27 KiB (new), 0 bytes (No change)