avformat/internal: Remove declaration for ff_format_io_close_default()

Forgotten in d6799ee0.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/internal.h

@@ -719,10 +719,6 @@ int ff_copy_whiteblacklists(AVFormatContext *dst, const AVFormatContext *src);
  */
 int ff_format_io_close(AVFormatContext *s, AVIOContext **pb);
 
-/* Default io_close callback, not to be used directly, use ff_format_io_close
- * instead. */
-void ff_format_io_close_default(AVFormatContext *s, AVIOContext *pb);
-
 /**
  * Utility function to check if the file uses http or https protocol
  *