Do not reset channel_layout to 0.

The channel_layout may have been set by the demuxer.

libavcodec/aacdec.c

@@ -251,8 +251,6 @@ static av_cold int output_configure(AACContext *ac,
         }
 
         memcpy(ac->tag_che_map, ac->che, 4 * MAX_ELEM_ID * sizeof(ac->che[0][0]));
-
-        avctx->channel_layout = 0;
     }
 
     avctx->channels = channels;