Fix app closing transition in multi-window

Previously we attempted to disable the app closing transition
in multi-window. However, that didn't work because the registered
remote animation was still registered on the ActivityRecord, even
if the activity was restarted, leading to passing a null handler
into post, and then the animation never started.

Enable it in multi-window and also fix the transition.

Test: Enter multi-window, go home
Change-Id: I4d5d46688310b61365ba954fb41811efa29e41a5
Fixes: 72525431