I'm about to update our utxo type, but Christian spotted that this is
part of the ABI for the hsm. So make that a private "hsm_utxo" type,
to insulate it from changes.
In particular, the HSM versions only contain the fields that the
hsm cares about, and the wire format is consistent (even though that
*did* include some of those fields, they are now dummies).
In the long term, this should be removed from the ABI: once we
no longer have "close_info" utxos, this information should already be
in the PSBT.
I tested this hadn't accidentally changed the wire format by disabling
version checks and using an old hsmd with the altered daemons and
running the test suite.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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