Do not guess the channel layout when getting its string value.

Originally committed as revision 19185 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/audioconvert.c

@@ -124,9 +124,6 @@ void avcodec_get_channel_layout_string(char *buf, int buf_size, int nb_channels,
 {
     int i;
 
-    if (channel_layout==0)
-        channel_layout = avcodec_guess_channel_layout(nb_channels, CODEC_ID_NONE, NULL);
-
     for (i=0; channel_layout_map[i].name; i++)
         if (nb_channels    == channel_layout_map[i].nb_channels &&
             channel_layout == channel_layout_map[i].layout) {