docs: def unsubscribe(self, connection, destination):
          """
          Unsubscribes a connection from the specified topic destination. 
  
          @param connection: The client connection to unsubscribe.
          @type connection: L{coilmq.server.StompConnection}
  
          @param destination: The topic destination (e.g. '/topic/foo')
          @type destination: C{str} 
          """
          self.log.debug("Unsubscribing %s from %s" % (connection, destination))
          if connection in self._topics[destination]:
              self._topics[destination].remove(connection)
  
          if not self._topics[destination]:
              del self._topics[destination]