Clean up docs on public chan_utils methods to be more useful

[TheBlueMatt]

No description provided.

[codecov]

Codecov Report

Merging #940 (2291457) into main (3996eaa) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 2291457 differs from pull request most recent head 8cdc855. Consider uploading reports for the commit 8cdc855 to get more accurate results

@@           Coverage Diff           @@
##             main     #940   +/-   ##
=======================================
  Coverage   90.59%   90.60%           
=======================================
  Files          60       60           
  Lines       30393    30393           
=======================================
+ Hits        27536    27538    +2     
+ Misses       2857     2855    -2     

Impacted Files	Coverage Δ
lightning/src/ln/chan_utils.rs	97.43% <100.00%> (ø)
lightning/src/ln/functional_tests.rs	97.20% <0.00%> (+0.03%)	⬆️

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[devrandom]

Lightning-signer is actually using these for test purposes, but I agree it doesn't make a lot of sense to expose and we can copy the small amount of code to our repo.

[TheBlueMatt]

Lightning-signer is actually using these for test purposes

Alright, no big deal, we can fix the docs instead of un-exposing :).

[valentinewallace]

Maybe both could use something about when/why you'd want to call them?

[jkczyz]

Looks good after squash

[TheBlueMatt]

Squashed without changes:

$ git diff-tree -U1 22914572f 8cdc855f0
$