Non-zero-fee anchors support was removed

[devrandom]

#1685 effectively removed support for non-zero-fee anchors. However, VLS still needs to support these for now, and we are using LDK utilities for transaction building.

Cc @wpaulino

[TheBlueMatt]

Hmm, we asked before we landed this and CLN folks (actually responded after #1685 (comment)) indicating it was okay to go ahead and CLN would be moving to 0-fee-htlc anchors ASAP so there's little reason to support this anymore.

I'm not super excited about adding parallel util methods to construct non-0-fee HTLC anchor txn just for something that won't go into prod.

CC @cdecker can we get some clarity on where y'all are with this?

[ariard]

From my memory, the non-0-fee HTLC anchor txn was ever only deployed by LND. option_anchors_zero_fee_htlc_tx was in nurturing before any other impl worked seriously on anchor support.

[devrandom]

From what I understand, CLN has only non-0-fee anchors right now.

[TheBlueMatt]

IIUC, when CLN implemented anchors they didn't actually (initially) implement spending anchors, just building the tx format but continuing to operate "as normal". This would mean that 0-fee HTLC txn wouldnt work, so they didn't go that way with their very first implementation.