11/n: Finish remainder of IFingerprint implementation

With the exception of invalidateAuthenticatorId, all IFingerprint
plumbing should be ready for testing.

Updates RemovalConsumer#onRemoved to allow nullable identifiers,
since enrollmentId=0 is now valid from the HAL.

Fixes: 170497736
Test: Enroll, auth, remove on existing devices
Change-Id: I070a5416a33e6aa926823a9babd3ae81238a3c08