bring back get_superevents call

gwcelery/tasks/superevents.py

@@ -101,8 +101,7 @@ def process(payload):
         superevent = _SuperEvent(s['t_start'],
                                  s['t_end'],
                                  s['t_0'],
-                                 s['superevent_id'],
-                                 s['preferred_event'], s)
+                                 s['superevent_id'])
         _update_superevent(superevent,
                            event_info,
                            t_0=t_0,