cmdutils: drop libavformat/network.h include

It is not a public header and has not been used since
10173c0e58

fftools/cmdutils.c

@@ -55,9 +55,6 @@
 #include "libavutil/ffversion.h"
 #include "libavutil/version.h"
 #include "cmdutils.h"
-#if CONFIG_NETWORK
-#include "libavformat/network.h"
-#endif
 #if HAVE_SYS_RESOURCE_H
 #include <sys/time.h>
 #include <sys/resource.h>