Fix flicker while booting

There was a short period of time where KeyguardScrim already went
away but status bar wasn't drawn yet, so we didn't consider it as
a wallpaper target so the wallpaper was invisible for a couple of
frames. Now only remove the scrim after the status bar has fully
drawn.

Change-Id: Ibf23b9e1277b6ce06e4ce70c9b7a5db9cbefce00
Fixes: 29643498