Handle a notification that a driver has been removed.

        Args:
            unused_channel: The message channel.
            data: The message data.

def xray_driver_removed_handler(self, unused_channel, data):
        """Handle a notification that a driver has been removed.

        Args:
            unused_channel: The message channel.
            data: The message data.
        """
        gcs_entries = ray.gcs_utils.GcsTableEntry.GetRootAsGcsTableEntry(
            data, 0)
        driver_data = gcs_entries.Entries(0)
        message = ray.gcs_utils.DriverTableData.GetRootAsDriverTableData(
            driver_data, 0)
        driver_id = message.DriverId()
        logger.info("Monitor: "
                    "XRay Driver {} has been removed.".format(
                        binary_to_hex(driver_id)))
        self._xray_clean_up_entries_for_driver(driver_id)