Remove failsafe runnable once the animation finishes.

- The scheduled failsafe runnable was running after we had already
  cleaned up the reference to the animation runner. Clear the runnable
  and also mark the animation as canceled so that future calls that
  happen to get through (from the runner as well) are also ignored.

Bug: 79514993
Test: atest FrameworksServicesTests:com.android.server.wm.RecentsAnimationControllerTest
Change-Id: Ib8d565022068833ccad212df3a7f6df68f5343d7