Clear out position-specific end actions in clearAnimator().

Previously, these were cleared in onAnimationEnd. This meant that any non-position animations started while a position animation was in progress would end up using leftover end actions, resulting in undefined behavior.

Fixes: 137201711
Test: atest SystemUITests
Change-Id: I19c2e847ae29681b30123afdf6e1e8f7a13e52ef