sipmlify plugins and tests and remove superflous core event

src/chat.rs

@@ -1980,13 +1980,6 @@ pub(crate) fn add_contact_to_chat_ex(
         msg.param.set_int(Param::Arg2, from_handshake.into());
 
         msg.id = send_msg(context, chat_id, &mut msg)?;
-    } else {
-        // send an event for unpromoted groups
-        // XXX probably not neccessary because ChatModified should suffice
-        context.call_cb(Event::MsgsChanged {
-            chat_id,
-            msg_id: MsgId::new(0),
-        });
     }
     context.call_cb(Event::ChatModified(chat_id));
     Ok(true)