Fix bug where fingerprint for wrong userId was attempted to be removed.

- cleaned up private API to ensure userId is distinct from groupId.
- fixed bug where we were sending the wrong userId when attempting to
- fix warning about wrong fingerId when receiving final id of 0.

Fixes bug 28268635

Change-Id: I9507723c1a763152775f2feff76c16762f23cf2d
6 files changed