Remove next_funding_txid tlv from Channel read/write

[dunxen]

Want to remove this before release so that we can work on a way to not persist this but rather get it from other persisted data and just free up the TLV.

Note that the "added in 0.0.124" comment was incorrect as it was actually added in #3137 but the comment was stale. So it's safe to remove.

See #3137 (comment) for context.

[optout21]

LGTM, minor comment regarding the commas

[dunxen]

LGTM, minor comment regarding the commas

Thanks. Done!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.24%. Comparing base (0c31021) to head (7177acb).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3417      +/-   ##
==========================================
+ Coverage   89.22%   89.24%   +0.02%     
==========================================
  Files         130      130              
  Lines      106965   106960       -5     
  Branches   106965   106960       -5     
==========================================
+ Hits        95438    95458      +20     
+ Misses       8734     8709      -25     
  Partials     2793     2793              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jkczyz]

LGTM. Could you please include the rationale in the commit message? Better to not rely on github for this information.

[dunxen]

LGTM. Could you please include the rationale in the commit message? Better to not rely on github for this information.

Yeah true, thanks! Done.

[TheBlueMatt]

Can we actually just remove the field entirely and use funding_tx.compute_txid() and the current channel state instead?

[dunxen]

Can we actually just remove the field entirely and use funding_tx.compute_txid() and the current channel state instead?

Yeah that's likely what we'll do. I just wanted to remove the persistence here to keep this small. I can address removing the field entirely in #3423.

[TheBlueMatt]

Alright, definitely need to figure it out before 0.1, though.

[dunxen]

Alright, definitely need to figure it out before 0.1, though.

Yeah, I'm adding it to #3423 which needs to go in before 0.1.