[MemoryLeak] Fix leak of FloatingRotationButton.mKeyButtonContainer from IRotationWatcher.Stub

Clear RotationButton and it's callbacks when RotationButtonController#onDestroy() is called.

Fix: 423710276
Flag: NONE - released code
Test: presubmit
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:83d205fa6f2a48a44484584e960eb848511bd546)
Merged-In: I7b1199496bdcc0fa6281c1d193362b00367f848e
Change-Id: I7b1199496bdcc0fa6281c1d193362b00367f848e