[repo] Clean up unused variables

[SimonCropp]

Fixes #
Design discussion issue #

Changes

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.40%. Comparing base (e5a7095) to head (83e612a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6100      +/-   ##
==========================================
- Coverage   86.40%   86.40%   -0.01%     
==========================================
  Files         257      257              
  Lines       11649    11648       -1     
==========================================
- Hits        10065    10064       -1     
  Misses       1584     1584              

Files with missing lines	Coverage Δ
...plementation/ZipkinActivityConversionExtensions.cs	95.76% <ø> (-0.04%)	⬇️