[Scrim] Remove notif scrim flicker on unlock

We just keep notif scrim alpha to 0 when we are on keyguard and we are
not transitioning to full shade. This will prevent the notification
shade from showing when tracking on the lockscreen.

Bug: 201040592
Test: Manual on devices of multiple form factors:
	Launch notif from LS - portrait and landscape
	Launch UserSwitcher From LS - portrait and landscape
	Show pin bouncer in LS
	Swipe to unlock - portrait and landscape

Change-Id: I0cfa7cd40b69c5c9ea7eeb708f1a073f307918cb