don't append to the activity stream on LDAP group disassociate

for organizations w/ a large number of ldap orgs/teams, this results in
a _huge_ number of extraneous activity stream entries

see: https://github.com/ansible/ansible-tower/issues/7655

awx/sso/backends.py

@@ -307,7 +307,7 @@ def _update_m2m_from_groups(user, ldap_user, rel, opts, remove=True):
                 should_add = True
     if should_add:
         rel.add(user)
-    elif remove:
+    elif remove and user in rel.all():
         rel.remove(user)