avformat/avio_internal: Don't include url.h

It is only included because two very rarely used functions
use pointers to URLContexts; use struct URLContext instead.
Also move ffio_geturlcontext() so that one can avoid
a forward declaration of struct URLContext (which would be
necessary as soon as FF_API_AVIODIRCONTEXT is no more).

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

libavformat/hls.c

@@ -43,6 +43,7 @@
 #include "internal.h"
 #include "avio_internal.h"
 #include "id3v2.h"
+#include "url.h"
 
 #include "hls_sample_encryption.h"