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>

tests/fuzz/fuzz-bolt12-invrequest-decode.c

@@ -1,4 +1,5 @@
 #include "config.h"
+#include <assert.h>
 #include <ccan/mem/mem.h>
 #include <common/bolt12.h>
 #include <common/utils.h>

tests/fuzz/libfuzz.h

@@ -4,6 +4,7 @@
 #include "config.h"
 #include <ccan/ccan/short_types/short_types.h>
 #include <ccan/ccan/tal/tal.h>
+#include <common/utils.h>
 #include <stddef.h>
 #include <stdint.h>