Revert^2 "Remove DepartingAnimationTarget from BackMotionEvent(2/2)"

This would create another SurfaceControl object through IPC, which is
unnecessary because the animation should run through
BackAnimationRunner.

Flag: com.android.window.flags.remove_depart_target_from_motion
Bug: 395035430
Test: execute back-to-home transition several times, verify no
predict_back animation leash left in offscreen layer.

Change-Id: Ib54380411438fc7169a37740bf09d7d83344f916