Turns out it's a single sig, identical to the already-handled
case where we spend a to_remote output.
We also close a temporary memleak: stack was unused, but
tallocated off the psbt, so it lives as long as the PSBT.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
1. anchor_to_remote_redeem => bitcoin_wscript_to_remote_anchored,
which matches other witness script producing functions and makes
it clear that it's a to_remote variant.
2. is_anchor_witness_script => is_to_remote_anchored_witness_script
makes it clear that it's about a to_remote output (as altered
when anchors are enabled) not an anchor output!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Libwally update breaks compatibility, so
we do this in one large step.
Changelog-Changed: JSON-RPC: elements network PSET now only supports PSETv2.
Changelog-Added: JSON-RPC: PSBTv2 supported for fundchannel_complete, openchannel_update, reserveinputs, sendpsbt, signpsbt, withdraw and unreserveinputs parameter psbt, openchannel_init and openchannel_bump parameter initialpsbt, openchannel_signed parameter signed_psbt and utxopsbt parameter utxopsbt
