Admin can remove anyone from any group.

Admins have the right to remove a member from a group
even if he is the only owner of that group.

This also fixes the original cause of the bug: An admin
can remove himself/herself from the admin group (which
doesn't have an owner)

Bug: 966312
Change-Id: Ibaf3a1f40d87b6c8422ca921725f354f5b0e3110
Merge "Admin can remove anyone from any group." into develop