1. Make FingerprintEnrollFinish stay on the back stack during "add
another"
2. Remove skip button from the enrolling screen, since the user can
now back out of the enrollment flow, or back to
FingerprintEnrollFinish and press "done" there.
Test: Run FingerprintEnrollFinishTest with `am instrument`
Bug: 32054268
Change-Id: Icaf017952d6582a14b4d0904b7ee67ad22e5280d
019593072b