Don't show lockscreen after using bouncer

When the bouncer is programatically invoked, the lockscreen content
will remain visible briefly after unlock. If the user swipes up to
show the bouncer, the animation runs correctly. Ensure the lockscreen
alpha is 0 during the PRIMARY_BOUNCER->GONE transition.

Fixes: 283226063
Test: atest PrimaryBouncerToGoneTransitionViewModelTest
Change-Id: I55257397dde6270c8340b6868c15839d75579ab6