Remove a11y noise for bouncer unlock

When the bouncer unlocks, the keyguard message are and the lock icon
view announce for accessibility but are not visible. By ensuring the
view is visible in order to announce for accessibility, when we unlock
the pin screen with talkback, we just get "Device unlocked"

Fixes: 284902478
Test: unlock pin screen with talkback.
Change-Id: I10c7e48e821e7eed1d85815cfb1b920b197f7350