V4L/DVB (4986): Removed unimplemented cx2341x API commands

The commands CX2341X_DEC_SET_AUDIO_OUTPUT, CX2341X_DEC_SET_AV_DELAY and
CX2341X_ENC_SET_3_2_PULLDOWN are not implemented in the Conexant firmware.
So these commands are removed. This also means that the V4L2_CID_MPEG_VIDEO_PULLDOWN
control in cx2341x.c and pvrusb2-hdw.c is removed.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>