Remove AppTransitionController

It is dead code since shell transition is enabled.

Also migrate some unit tests to use shell transition.
For example, some visibility tests rely on
ActivityRecord#deferCommitVisibilityChange
while mTransitionController.isShellTransitionsEnabled() is false
if registerTransitionPlayer is not called.

Bug: 365884835
Flag: EXEMPT remove outdated code
Test: atest ActivityRecordTests

Change-Id: I8e7c7c6a24f5e40fb93919f3b95b443a21beb514