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

doc/examples/avio_reading.c

@@ -74,9 +74,6 @@ int main(int argc, char *argv[])
     }
     input_filename = argv[1];
 
-    /* register codecs and formats and other lavf/lavc components*/
-    av_register_all();
-
     /* slurp file content into buffer */
     ret = av_file_map(input_filename, &buffer, &buffer_size, 0, NULL);
     if (ret < 0)