Remove unnecessary parentheses around return statements (#5931)

Python will return a tuple whether there are parentheses around the returned values or not.

I'm just sick of my editor complaining about this all over the place :)

tests/test_state.py

@@ -106,7 +106,7 @@ class StateGroupStore(object):
         }
 
     def get_state_group_delta(self, name):
-        return (None, None)
+        return None, None
 
     def register_events(self, events):
         for e in events: