No-op an unused API for Shell Transitions

Another api was added to RecentsAnimationController but this doesn't
have a use in Shell Transitions. It was causing a crash though, so
override it to be a no-op.

Bug: 183993924
Test: open app, go to recents, go back, observe no crash
Change-Id: I3ece5b927c8c7d27252f185ed421112fea5f12c1