net: usbnet: remove driver version

Obviously this driver version doesn't make sense. Go with the default
and let ethtool display the kernel version.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>