docs: def disconnect(self, connection):
          """
          Removes a subscriber connection.
  
          @param connection: The client connection to unsubscribe.
          @type connection: L{coilmq.server.StompConnection}
          """
          self.log.debug("Disconnecting %s" % connection)
          for dest in list(self._topics.keys()):
              if connection in self._topics[dest]:
                  self._topics[dest].remove(connection)
              if not self._topics[dest]:
                  # This won't trigger RuntimeError, since we're using keys()
                  del self._topics[dest]