mfenc: Remove an unused include

This might have been used originally for the decoder parts of
the MediaFoundation wrapper, which aren't merged yet.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/mfenc.c

@@ -26,9 +26,7 @@
 #include "libavutil/imgutils.h"
 #include "libavutil/opt.h"
 #include "libavutil/time.h"
-
-// Include after mf_utils.h due to Windows include mess.
-#include "mpeg4audio.h"
+#include "internal.h"
 
 typedef struct MFContext {
     AVClass *av_class;