code: def remove_callback(self, fd, handle):
          
          if self._mpoll is None:
              raise RuntimeError('Poller instance is closed')
          mpoll = self._mpoll.get(fd)
          if mpoll is None:
              raise ValueError('not watching fd {}'.format(fd))
          mpoll.remove_callback(handle)
docs: Remove a callback added by :meth:`~Poller.add_callback`.
  
          If this is the last callback that is registered for the fd then this
          will deallocate the ``MultiPoll`` instance and close the libuv handle.