Update CHANGELOG

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CHANGELOG

@@ -11,7 +11,6 @@ v 8.4.0 (unreleased)
   - Add CAS support (tduehr)
   - Add link to merge request on build detail page
   - Revert back upvote and downvote button to the issue and MR pages
-  - Enable "Add key" button when user fills in a proper key (Stan Hu)
   - Swap position of Assignee and Author selector on Issueables (Zeger-Jan van de Weg)
 v 8.3.3 (unreleased)