refactor(api)!: remove exported.CounterpartyChannelI interface

[colin-axner]

Description

More code cleanup

closes: #XXXX

Commit Message / Changelog Entry

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Before we can merge this PR, please make sure that all the following items have been
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• Targeted PR against the correct branch (see CONTRIBUTING.md).
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards and Go style guide.
• Wrote unit and integration tests.
• Updated relevant documentation (docs/) or specification (x/<module>/spec/).
• Added relevant godoc comments.
• Provide a commit message to be used for the changelog entry in the PR description for review.
• Re-reviewed Files changed in the Github PR explorer.
• Review Codecov Report in the comment section below once CI passes.

[DimitrisJim]

lgtm pending CI picking up any stale references

[damiannolan]

🚀

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (310a4bd) 81.49% compared to head (d59489e) 81.53%.
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5744      +/-   ##
==========================================
+ Coverage   81.49%   81.53%   +0.04%     
==========================================
  Files         199      199              
  Lines       15203    15216      +13     
==========================================
+ Hits        12389    12406      +17     
+ Misses       2348     2344       -4     
  Partials      466      466              

Files	Coverage Δ
modules/apps/transfer/keeper/relay.go	90.94% <100.00%> (ø)
modules/core/04-channel/keeper/keeper.go	90.84% <100.00%> (+0.06%)	⬆️
modules/core/04-channel/keeper/upgrade.go	92.52% <100.00%> (+0.21%)	⬆️
modules/core/04-channel/types/channel.go	100.00% <ø> (+6.15%)	⬆️
modules/core/04-channel/types/codec.go	100.00% <ø> (ø)