audio_format: remove the packed S24 format

For simplicity, the MPD core should not have to deal with packing.  It
is rarely used, and those plugins that need it should use the
pcm_export library instead.

src/audio_parser.c

@@ -116,11 +116,11 @@ parse_sample_format(const char *src, bool mask,
 		break;
 
 	case 24:
-		if (memcmp(endptr, "_3", 2) == 0) {
-			sample_format = SAMPLE_FORMAT_S24;
+		if (memcmp(endptr, "_3", 2) == 0)
+			/* for backwards compatibility */
 			endptr += 2;
-		} else
-			sample_format = SAMPLE_FORMAT_S24_P32;
+
+		sample_format = SAMPLE_FORMAT_S24_P32;
 		break;
 
 	case 32: