Remove old demuxers

Delete demux_avi, demux_asf, demux_mpg, demux_ts. libavformat does
better than them (except in rare corner cases), and the demuxers have
a bad influence on the rest of the code. Often they don't output
proper packets, and require additional audio and video parsing. Most
work only in --no-correct-pts mode.

Remove them to facilitate further cleanups.

audio/decode/dec_audio.c

@@ -21,6 +21,8 @@
 #include <unistd.h>
 #include <assert.h>
 
+#include <libavutil/mem.h>
+
 #include "demux/codec_tags.h"
 
 #include "config.h"