Remove sound support

Two reasons for removing it:

    1) I won't ever want to hear useless sounds

    2) The sound support is a bit of a joke. The code is there but you have
       to hunt it somewhere else (not in any repository that I know of).
       In my 10 years of using wmaker, I never used it for this reason.
       Now I consider having no sound in Window Maker a feature, and I like
       it that way. So there is no point in carrying useless code around.

PS: There is still the code in WPrefs to be removed.

src/defaults.c

@@ -440,8 +440,6 @@ WDefaultEntry optionList[] = {
 	 &wPreferences.use_saveunders, getBool, NULL},
 	{"OpaqueMove", "NO", NULL,
 	 &wPreferences.opaque_move, getBool, NULL},
-	{"DisableSound", "NO", NULL,
-	 &wPreferences.no_sound, getBool, NULL},
 	{"DisableAnimations", "NO", NULL,
 	 &wPreferences.no_animations, getBool, NULL},
 	{"DontLinkWorkspaces", "NO", NULL,