Enable fingerprint cleanup upon connection to daemon and upon user switches

Simplify and cleaned up enumeration code by only doing single-user
enumeration

Fixes: 63606218

Test: The enumerate path was already tested in b/35358801
Test: Modify FingerprintUtils to cause inconsistency between framework
      and hardware, then do manual test
Test: Enumerate occurs when (re)connecting to fingerprint daemon, and
      also whenever user switching occurs. Looked at timings in logs,
      and it shouldn't be possible to switch user while cleanup is in
      progress

Change-Id: Ibc2bbe98d4137e7de60a7fcda29c9fef803048b9