Fix alternateBouncer => primaryBouncer flicker

Don't update the scrim state between
hiding the alternate bouncer and showing the
primary bouncer. This can cause the scrim state to
transition to the UNLOCKED scrim between AUTH_SCRIMMED_SHADE
and BOUNCER_SCRIMMED.

Test: atest StatusBarKeyguardViewManagerTest
Bug: 272744555
Bug: 272350664
Change-Id: I1c68ceb9bb77b0b664ca351af1a897b835e80367