usb: kbd: Do not deregister usbkbd twice when using dm

The dm usb_kbd_remove function() will deregister the usb keyboard for
us on a "usb reset" / "usb stop" so there is no need to manually call
usb_kbd_deregister() in the dm case.

This commit removes usb_kbd_deregister() in the dm case fixing the
following "usb reset" errors:

usb_kbd_remove: warning, ret=-6
device_remove: Device 'usb_kbd' failed to remove, but children are gone

Signed-off-by: Hans de Goede <hdegoede@redhat.com>