Implement site deregistration

django_backend/backend/models.py

@@ -229,7 +229,7 @@ class RabbitMQInstance(SingletonModel):
         LOGGER.info(self._msg('updated permissions for {}'.format(site.client)))
 
     def deregister_site(self, site):
-        # TODO implement
+        self._delete_user(site)
         LOGGER.info(self._msg('deregistered {}'.format(site.client)))
 
     def is_client_connected(self, site):