staging: r8188eu: remove unused functions from os_dep/ioctl_linux.c

Remove unused functions that are now no longer called as a result of the
removal of rtw_ioctl in a previous patch. This includes functions not
directly called from rtw_ioctl, but anything in that specific
call-chain.
Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210810235047.177883-2-phil@philpotter.co.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>