code: async def remove_listener(self, channel, callback):
          
          if self.is_closed():
              return
          if channel not in self._listeners:
              return
          if callback not in self._listeners[channel]:
              return
          self._listeners[channel].remove(callback)
          if not self._listeners[channel]:
              del self._listeners[channel]
              await self.fetch('UNLISTEN {}'.format(utils._quote_ident(channel)))
docs: Remove a listening callback on the specified channel.