code: def remove_done_callback(self, func):
          
          if self._done is None or self._done.is_set():
              raise ValueError("Process is complete.")
          self._callbacks = [c for c in self._callbacks if c != func]
docs: Remove a callback from the long running operation.
  
          :param callable func: The function to be removed from the callbacks.
          :raises: ValueError if the long running operation has already
           completed.