aaa: remove user/group sync

Since all queries are performed using the engine sessions
table, the users groups are always derived from the principal
on user login there is no need to periodically sync users.
The groupids is updated on user login

Change-Id: I15248a628647430d7f3d22e68e66456caffbcb40
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1176306
Signed-off-by: Ravi Nori <rnori@redhat.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>