code: def listener_delete_event(self, listener_info):
          
          lb_list = self.neutronclient.list_loadbalancers()
          for lb in lb_list.get('loadbalancers'):
              if not lb.get("listeners"):
                  lb_id = lb.get('id')
                  LOG.info("Deleting lb %s port" % lb_id)
                  self.delete_lbaas_port(lb_id)
docs: Process listener delete event.
  
          This is lbaas v2
          vif will be plugged into ovs when first
          listener is created and unpluged from ovs
          when last listener is deleted.
          as the data only contains listener id, we will
          scan all loadbalancers from db and delete the vdp
          if their admin state is down in that loadbalancer