notifications: Elimininate now-unnecessary database query.

Because we're passing through the trigger for notifications to
do_send_missedmessage_events_reply_in_zulip, we don't need to go back
to the database to determine which messages actually mentioned the
user.

zerver/lib/notifications.py

@@ -361,14 +361,14 @@ def do_send_missedmessage_events_reply_in_zulip(user_profile: UserProfile,
             context.update({'huddle_display_name': huddle_display_name})
     elif (missed_messages[0]['message'].recipient.type == Recipient.PERSONAL):
         context.update({'private_message': True})
-    else:
+    elif context['mention']:
         # Keep only the senders who actually mentioned the user
-        #
-        # TODO: When we add wildcard mentions that send emails, add
-        # them to the filter here.
-        senders = list(set(m['message'].sender for m in missed_messages if
-                           UserMessage.objects.filter(message=m['message'], user_profile=user_profile,
-                                                      flags=UserMessage.flags.mentioned).exists()))
+        senders = list(set(m['message'].sender for m in missed_messages
+                           if m['trigger'] == 'mentioned'))
+        # TODO: When we add wildcard mentions that send emails, we
+        # should make sure the right logic applies here.
+    else:
+        raise AssertionError("Invalid messages!")
 
     # If message content is disabled, then flush all information we pass to email.
     if not user_profile.message_content_in_email_notifications: