USB: serial: metro-usb: drop unused interrupt-out callback

Drop the unused interrupt-out callback.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/metro-usb.c

@@ -161,14 +161,6 @@ exit:
 			__func__, result);
 }
 
-static void metrousb_write_int_callback(struct urb *urb)
-{
-	struct usb_serial_port *port = urb->context;
-
-	dev_warn(&port->dev, "%s not implemented yet.\n",
-		__func__);
-}
-
 static void metrousb_cleanup(struct usb_serial_port *port)
 {
 	dev_dbg(&port->dev, "%s\n", __func__);
@@ -377,7 +369,6 @@ static struct usb_serial_driver metrousb_device = {
 	.open			= metrousb_open,
 	.close			= metrousb_cleanup,
 	.read_int_callback	= metrousb_read_int_callback,
-	.write_int_callback	= metrousb_write_int_callback,
 	.port_probe		= metrousb_port_probe,
 	.port_remove		= metrousb_port_remove,
 	.throttle		= metrousb_throttle,