Suppressing FUL after going to backup fixes b/7449820

Face Unlock would reappear when rotating a tablet after it had already
fallen back to the backup unlock method.  This change suppresses Face
Unlock after going to the backup so it isn't seen again until the user
leaves and revisits keyguard.

This change also removes the exposeFallback() callback from Face
Unlock.  It has been unnecessary for a long tiem since Face Unlock no
longer covers the backup.  The Face Unlock service was therefore
making unnecesaary calls via the AIDL interface.

Note that the AIDL interface change broke obsolete keyguard stuff.
That is being deleted soon anyway, so code has just been commented out
of the obsolete files to make it compile.

Change-Id: Ia5c451cce1703b3bc03e27a35c6b38373e944d1b