Cleanup includes

Improved manually with the help of neovim LSP warnings and iwyu:

    iwyu -Ibuilddir/app/ -Iapp/src/ app/src/XXX.c

app/src/decoder.h

@@ -3,13 +3,11 @@
 
 #include "common.h"
 
+#include <libavcodec/avcodec.h>
+
 #include "trait/frame_source.h"
 #include "trait/packet_sink.h"
 
-#include <stdbool.h>
-#include <libavcodec/avcodec.h>
-#include <libavformat/avformat.h>
-
 struct sc_decoder {
     struct sc_packet_sink packet_sink; // packet sink trait
     struct sc_frame_source frame_source; // frame source trait