examples: Don't call deprecated functions which don't do anything

doc/examples/demuxing_decoding.c

@@ -252,9 +252,6 @@ int main (int argc, char **argv)
     video_dst_filename = argv[2];
     audio_dst_filename = argv[3];
 
-    /* register all formats and codecs */
-    av_register_all();
-
     /* open input file, and allocate format context */
     if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
         fprintf(stderr, "Could not open source file %s\n", src_filename);