Revert "ALSA: HDA: Create mixers on ALC887"

This reverts commit 03b7a1ab.

This commit was mistakenly re-introduced.  While the change is harmless
(as ALC887 uses patch_alc888() now), we should get rid of any wrong code.

Signed-off-by: Takashi Iwai <tiwai@suse.de>