🐛 Talk slots were not removed upon withdrawal via speaker

Via organisers it worked. Closes #775

doc/changelog.rst

@@ -3,6 +3,7 @@
 Release Notes
 =============
 
+- :bug:`775` When a speaker withdrew their already-accepted talk, the talk slot was not removed from the schedule editor. It did work when setting the state via the organiser interface.
 - :bug:`774` The API endpoint for events always returned a 404 on the detail view, even when event was visible in the list view.
 - :feature:`-` Speaker and talk detail pages now contain links to their respective API detail pages as alternate links.
 - :feature:`-` The main schedule page now returns a 303 See Also redirect if accessed with JSON or XML accept headers.

src/pretalx/cfp/views/user.py

@@ -149,8 +149,7 @@ def post(self, request, *args, **kwargs):
                         url=obj.orga_urls.edit.full(),
                     )
                 )
-            obj.state = SubmissionStates.WITHDRAWN
-            obj.save(update_fields=['state'])
+            obj.withdraw(person=request.user)
             messages.success(self.request, phrases.cfp.submission_withdrawn)
         else:
             messages.error(self.request, phrases.cfp.submission_not_withdrawn)