Fix collaborative channel close amounts

[luckysori]

Fixes https://github.com/itchysats/10101/issues/475.

They were wrong because of a bug in our fork of rust-lightning: the channel amounts were not being updated after the custom output was removed.

We were already constructing the correct commitment transaction and because we only ever tested using force-close it looked like everything was working as intended!

[luckysori]

bors r+

[bors[bot]]

Build succeeded:

• CI
• formatting
• lint-commits