avcodec/avcodec: Don't include errno.h

This inclusion has been added before libavutil/error.h was split off
from avcodec.h (in 60c144f700).

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

libavcodec/avcodec.h

@@ -27,7 +27,6 @@
  * Libavcodec external API header
  */
 
-#include <errno.h>
 #include "libavutil/samplefmt.h"
 #include "libavutil/attributes.h"
 #include "libavutil/avutil.h"