ActiveDirectoryDsc: Update CHANGELOG.md for 6.1.0 Retracted Release

[X-Guardian]

Pull Request (PR) description

This PR updates the CHANGELOG.md for the 6.1.0 retracted release.

This Pull Request (PR) fixes the following issues

None

Task list

• [x] Added an entry to the change log under the Unreleased section of the file CHANGELOG.md. Entry should say what was changed and how that affects users (if applicable), and reference the issue being resolved (if applicable).
• [ ] Resource documentation added/updated in README.md.
• [ ] Resource parameter descriptions added/updated in README.md, schema.mof and comment-based help.
• [ ] Comment-based help added/updated.
• [ ] Localization strings added/updated in all localization files as appropriate.
• [ ] Examples appropriately added/updated.
• [ ] Unit tests added/updated. See DSC Community Testing Guidelines.
• [ ] Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• [ ] New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[codecov[bot]]

Codecov Report

Merging #640 (e9e8c67) into master (87b1308) will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #640   +/-   ##
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  Coverage      97%    97%           
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  Files          25     25           
  Lines        3384   3384           
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  Hits         3316   3316           
  Misses         68     68