feat: remove deprecated platform ubuntu

[erisu]

Platforms affected

n/a

Motivation, Context & Description

Remove deprecated/archived platform ubuntu from coho. This platform no longer is supported and does not recieve updates.

Testing

n/a

Checklist

• [ ] I've run the tests to see all new and existing tests pass
• [ ] I added automated test coverage as appropriate for this change
• [ ] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [ ] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [ ] I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #319 (89a5d15) into master (6375e78) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #319   +/-   ##
=======================================
  Coverage   58.85%   58.85%           
=======================================
  Files           8        8           
  Lines         491      491           
=======================================
  Hits          289      289           
  Misses        202      202           

Impacted Files	Coverage Δ
src/repoutil.js	68.91% <ø> (ø)

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