avformat/avienc: Remove superfluous header

04d2540c added intreadwrite.h to avienc.c, although there was (and is)
no need to do so. The inclusion seems to be a mistake as this commit
added a AV_WL32 to avidec.c.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/avienc.c

@@ -31,7 +31,6 @@
 #include "libavutil/avstring.h"
 #include "libavutil/avutil.h"
 #include "libavutil/internal.h"
-#include "libavutil/intreadwrite.h"
 #include "libavutil/dict.h"
 #include "libavutil/avassert.h"
 #include "libavutil/timestamp.h"