Remove "Front Playback Volume" and "Front Playback Switch" from emu10k1 only
for STAC9758/59

Since commit 7eae36fb
      "Fix the confliction of 'Front' control",
the "Front Playback Volume" control created by commit
	edf8e456
	"emu10k1: Front channels via fxbus 8 and 9"
was removed

"Front Playback Volume" and "Surround Playback Volume" have same dB range
since I2S DAC of SB Live! and SB Live! Platinum does not has any hardware
volume control.
Signed-off-by: Raymond Yau <superquad.vortex2@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>