tools: Drop a stale header

tools/graph2dot.c

@@ -28,7 +28,6 @@
 #include "libavutil/channel_layout.h"
 #include "libavutil/mem.h"
 #include "libavutil/pixdesc.h"
-#include "libavutil/audioconvert.h"
 #include "libavfilter/avfilter.h"
 
 #if !HAVE_GETOPT