we used this originally to suppress duplicate issuance of coin-move
events; we're assuming that any plugin expects duplicate events though
(and knows how to de-dupe them), so we no longer need this logic.
This makes init a two-stage, and causes some code hoisting.
And we can now send all the HTLCs in a single message, since we have
an 128MB limit and each HTLC is 37 bytes.
This breaks the onchaind stresstest, which uses canned internal messages.
It's time to finally delete that.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
