CHORE: update CHANGELOG for v0.16.1

[pyansys-ci-bot]

Update CHANGELOG for v0.16.1 and remove .md files in doc/changelog.d.

Caution

Do not merge this pull request until the release has been successfully made.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.66%. Comparing base (b3713a2) to head (1f427f6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6098      +/-   ##
==========================================
- Coverage   85.66%   85.66%   -0.01%     
==========================================
  Files         166      166              
  Lines       62786    62786              
==========================================
- Hits        53788    53787       -1     
- Misses       8998     8999       +1     

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