aaa: remove group should not depend on existence of provider

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1120720
Change-Id: Idd8a5a35816a530dbb7405eedefe4936b7e91c4f
Topic: AAA
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>