Remove "Master Mono Playback Volume" and "Master Mono Playback Switch"
of ac97 mixer since au88x0 does no use "Master Mono Pin" of AC97 codec
even au88x0 support mono playback
Signed-off-by: Raymond Yau <superquad.vortex2@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>