code: def _remove_multicast_group(self, datapath, outport, dst):
          
          ofproto = datapath.ofproto
          parser = datapath.ofproto_parser
          dpid = datapath.id
  
          self._send_event(
              EventMulticastGroupStateChanged(
                  MG_GROUP_REMOVED, dst, outport, []))
          self._del_flow_entry(datapath, outport, dst)
          for port in self._to_hosts[dpid][dst]['ports']:
              self._del_flow_entry(datapath, port, dst)
          leave = self._to_hosts[dpid][dst]['leave']
          if leave:
              if ofproto.OFP_VERSION == ofproto_v1_0.OFP_VERSION:
                  in_port = leave.in_port
              else:
                  in_port = leave.match['in_port']
              actions = [parser.OFPActionOutput(outport)]
              self._do_packet_out(
                  datapath, leave.data, in_port, actions)
docs: remove flow entries about the group and send a LEAVE message
          if exists.