s1d13xxxfb: drop unused code

Silence warnings such as -

drivers/video/s1d13xxxfb.c:421: warning: ‘bltbit_wait_bitset’ defined but not used

Just drop the unused code.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>