global: remove unnecessary includes from headers.

Each header should only include the other headers it needs to compile;
`devtools/reduce-includes.sh */*.h` does this.  The C files then need
additional includes if they don't compile.

And remove the entirely useless wire/onion_wire.h, which only serves to include wire/onion_wiregen.h.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/mkencoded.c

@@ -4,6 +4,7 @@
 #include <ccan/err/err.h>
 #include <ccan/str/hex/hex.h>
 #include <common/decode_array.h>
+#include <common/utils.h>
 #include <stdio.h>
 
 static NORETURN void usage(void)