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>

common/cryptomsg.c

@@ -1,5 +1,6 @@
 #include "config.h"
 #include <assert.h>
+#include <ccan/build_assert/build_assert.h>
 #include <ccan/crypto/hkdf_sha256/hkdf_sha256.h>
 #include <ccan/mem/mem.h>
 #include <common/cryptomsg.h>