Fix ActivityRecord leak if mainWindow is animating.

For CTS test, sometimes remove starting window won't pass throught
WS#removeIfPossible if the binder was dead before reveal animation
finish. For this case, cancel reveal animation in WS#removeIfPossible
if it's animating reveal animation.

Bug: 184830058
Bug: 188245125
Bug: 188244674
Test: verify from bugreport that no systemui crash after WM's CTS.
Test: run atest StartActivityTests then verify no activity leaked.
Change-Id: I81484870ff89a78b6133be03d439d45d550bdd8c