Remove/replace some unnecessary avcodec.h inclusions

Also remove other unnecessary headers and include headers directly while
at it.

Signed-off-by: Andreas Rheinhardt <[email protected]>
diff --git a/libavcodec/mpegaudiodecheader.h b/libavcodec/mpegaudiodecheader.h
index 1da2a4c..ed5d1f3 100644
--- a/libavcodec/mpegaudiodecheader.h
+++ b/libavcodec/mpegaudiodecheader.h
@@ -27,7 +27,8 @@
 #ifndef AVCODEC_MPEGAUDIODECHEADER_H
 #define AVCODEC_MPEGAUDIODECHEADER_H
 
-#include "avcodec.h"
+#include <stdint.h>
+#include "codec_id.h"
 
 #define MP3_MASK 0xFFFE0CCF