usb: gadget: printer: remove unused and empty printer_unbind

The unbind() method is optional is usb_composite_driver.
In this particular driver the method does nothing so it can be removed.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
1 file changed