We alternated between using a sha256 and using a privkey, but there are
numerous places where we have a random 32 bytes which are neither.
This fixes many of them (plus, struct privkey is now defined in terms of
struct secret).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
We remove the unused status_send_fd, and rename status_send_sync (it
should only be used for that case now).
We add a status_setup_async(), and wire things internally to use that
if it's set up: status_setup() is renamed status_setup_sync().
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>