Use UnlockMethodCache#canSkipBouncer in user switcher

KeyguardMonitor#canSkipBouncer was not updated properly when the phone
was unlocked using fingerprint.

This CL removes that method and changes UserSwitcherController to query
UnlockMethodCache directly, as it was KeyguardMonitor's only client for
that method.

Test: manual unlocking with FP and with pattern
Test: no automated test yet
Bug: 140486529
Merged-In: Idbff4fbabca962c632ff5d78b25418c0502db9a7
Change-Id: Idbff4fbabca962c632ff5d78b25418c0502db9a7
(cherry picked from commit d2eb34b6)