android build: exclude kivy classes from qml apk

taken from #8545
22bfd4e

note: com.android.support is used in our p4a fork's PythonActivity.java
(com.android.support was previously pulled in by me.dm7.barcodescanner)
https://github.com/accumulator/python-for-android/blob/052b9f7945bae557347fa4a4b418040d9da9eaff/pythonforandroid/bootstraps/qt5/build/src/main/java/org/kivy/android/PythonActivity.java#L43

contrib/android/buildozer_qml.spec

@@ -138,11 +138,9 @@ android.add_jars = .buildozer/android/platform/*/build/libs_collections/Electrum
 
 # (list) List of Java files to add to the android project (can be java or a
 # directory containing the files)
-android.add_src = electrum/gui/kivy/data/java-classes/
-
-android.gradle_dependencies = me.dm7.barcodescanner:zxing:1.9.8
-
-android.add_activities = org.electrum.qr.SimpleScannerActivity
+# android.add_src = ...
+# android.add_activities = ...
+android.gradle_dependencies = com.android.support:support-compat:28.0.0
 
 # (str) python-for-android branch to use, if not master, useful to try
 # not yet merged features.