Cleanup legacy preemption logic

[gabesaba]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Cleanup MultiplePreemptions=false branch. Simplify code base.

Which issue(s) this PR fixes:

Fixes #3601

Special notes for your reviewer:

Does this PR introduce a user-facing change?

We deprecate legacy preemption logic, with MultiplePreemptions being the only behavior 

[k8s-ci-robot]

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[gabesaba]

I can try to salvage these tests, if you think they're worth keeping. Let me know what you think, reviewers

[mimowo]

Thank you for the cleanup. It basically means MultiplePreemptions is graduated to stable, so we should reflect that in the kube_features. cc @tenzen-y ?

EDIT: what we typically do is we set the feature gate to stable, but keep it declared, so that users are not broken on upgrade if they have --feature-gate=MultiplePreemptions=true. Then we drop the declaration one or two releases later.

[mimowo]

I think we shouldn't be cleaning up the logic while keeping the feature in Beta. I would be supportive of turning the PR into a feature which graduates the feature gate to stable.

[tenzen-y]

Thank you for the cleanup. It basically means MultiplePreemptions is graduated to stable, so we should reflect that in the kube_features. cc @tenzen-y ?

EDIT: what we typically do is we set the feature gate to stable, but keep it declared, so that users are not broken on upgrade if they have --feature-gate=MultiplePreemptions=true. Then we drop the declaration one or two releases later.

Yes, we should keep the feature gate for a while like 2 minor versions.

[mimowo]

@gabesaba please update it in kube_features, and just add a comment, "// remove in 1.12"

[k8s-ci-robot]

PR needs rebase.

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