USB: sis FB driver: *_ioctl32_conversion functions do not exist in recent kernels

Remove dead code while at it.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Cc: Greg KH <greg@kroah.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>