staging: r8188eu: remove private ioctls that return -1

Remove the private ioctls that are mapped to rtw_wx_priv_null.
rtw_wx_priv_null itself can also be removed.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211226212535.197989-6-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>