media: dvb: get rid of VIDEO_SET_SPU_PALETTE

No upstream drivers use it. It doesn't make any sense to have
a compat32 code for something that nobody uses upstream.

Reported-by: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>