events: Remove "color" from event_dict

We are going to feed internal and external events as separat event
sources to the FullCalendar. It is more efficient to specify the color
for the whole event source. So remove it from what get_dict returns for
an event.

mpicms/events/models.py

@@ -76,7 +76,6 @@ def get_dict(self, request=None):
             'start': self.start.isoformat(),
             'end': self.end.isoformat() if self.end else None,
             'url': self.get_url(request=request),
-            'color': '#aa0000' if self.external else '#006c66'
         }
 
     def clean(self):