ALSA: hda - Remove beep_mode=2

The beep_mode=2 option was introduced to make the beep mixer
controlling the beep input allocation/deallocation dynamically, so
that a user can switch between HD-audio codec digital beep and the
system beep only via mixer API.  This was necessary because the
keyboard driver took only the first input beep instance at that time.

However, the recent keyboard driver already processes the multiple
input instances, thus there is no point to keep this mode.

Let's remove it.

Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -875,8 +875,7 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
     		setup before initializing the codecs.  This option is
 		available only when CONFIG_SND_HDA_PATCH_LOADER=y is set.
 		See HD-Audio.txt for details.
-    beep_mode	- Selects the beep registration mode (0=off, 1=on, 2=
-		dynamic registration via mute switch on/off); the default
+    beep_mode	- Selects the beep registration mode (0=off, 1=on); default
 		value is set via CONFIG_SND_HDA_INPUT_BEEP_MODE kconfig.
     
     [Single (global) options]