Remove notifications on receiving own sent carbon copies

Notifications for a JID are removed when we see activity
in the form of a sent carbon copie from one of our other devices.

If we receive such carbon copies we can conclude that the message
we received earlier was answered from one of our other devices.

src/session.py

@@ -251,6 +251,7 @@ class ChatControlSession(stanza_session.EncryptedStanzaSession):
             # Its a Carbon Copied Message we sent
             obj.show_in_roster = False
             obj.show_in_systray = False
+            gajim.events.remove_events(self.conn.name, fjid, types=['chat'])
         else:
             # Everything else
             obj.show_in_roster = notify.get_show_in_roster(event_type,