net: usb: usb: remove old api ethtool_{get|set}_settings

The function usbnet_{get|set}_settings is no longer used,
so we remove it.

Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>