Remove a message callback previously registered with
        message_callback_add().

def message_callback_remove(self, sub):
        """Remove a message callback previously registered with
        message_callback_add()."""
        if sub is None:
            raise ValueError("sub must defined.")

        self._callback_mutex.acquire()
        for i in range(0, len(self.on_message_filtered)):
            if self.on_message_filtered[i][0] == sub:
                self.on_message_filtered.pop(i)
                self._callback_mutex.release()
                return
        self._callback_mutex.release()