Correctly disposing of LauncherUnlockAnimationController

In SystemUiProxy we don't need to check for null before calling
setLauncherUnlockAnimationController becase that function is already
checkingh fo nulls, so it was preventing the variable from getting
cleaned.

Fix: 275418590
Test: flake should dissapear or be reduced
Change-Id: I8cf5dad57678493167354e137a18e37b37f3e58b