avio: deprecate url_fileno

It's an evil hack that assumes an AVIOContext is always based on top of
an URLContext.
It's also not used anywhere.
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavformat/avio.h

@@ -623,9 +623,10 @@ int url_resetbuf(AVIOContext *s, int flags);
 int avio_open(AVIOContext **s, const char *url, int flags);
 
 int avio_close(AVIOContext *s);
-URLContext *url_fileno(AVIOContext *s);
 
 #if FF_API_OLD_AVIO
+attribute_deprecated URLContext *url_fileno(AVIOContext *s);
+
 /**
  * @deprecated use AVIOContext.max_packet_size directly.
  */

libavformat/aviobuf.c

@@ -923,10 +923,12 @@ int avio_close(AVIOContext *s)
     return url_close(h);
 }
 
+#if FF_API_OLD_AVIO
 URLContext *url_fileno(AVIOContext *s)
 {
     return s->opaque;
 }
+#endif
 
 int avio_printf(AVIOContext *s, const char *fmt, ...)
 {