[event] People with only deleted submissions are no speakers

Closes #572

doc/changelog.rst

@@ -3,6 +3,7 @@
 Release Notes
 =============
 
+- :bug:`572` People who had only deleted submissions in an event were still shown in the submitter list, which was unexpected and was since fixed.
 - :feature:`-` If only one conference language is available, pretalx doesn't as speakers to choose it from a drop-down, as this behaviour is rather silly.
 - :support:`-` pretalx doesn't run ``regenerate_css`` on startup automatically any longer. This reduces startup times. If for any reason an event does not look as it should, you can fix it by running ``python -m pretalx regenerate_css``.
 - :feature:`-` You can now decide if you want to notify speakers about their changed talks when releasing a new schedule.

src/pretalx/event/models/event.py

@@ -471,7 +471,7 @@ def speakers(self):
     def submitters(self):
         from pretalx.person.models import User
 
-        return User.objects.filter(submissions__event=self).order_by('id').distinct()
+        return User.objects.filter(submissions__in=self.submissions.all()).order_by('id').distinct()
 
     def get_date_range_display(self) -> str:
         return daterange(self.date_from, self.date_to)