Remove duplicate CHANGELOG etnries

[ci skip]

CHANGELOG

@@ -3,8 +3,6 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.2.0 (unreleased)
   - Added a GitLab specific profiling tool called "Sherlock" (see GitLab CE merge request #1749)
   - Upgrade gitlab_git to 7.2.20 and rugged to 0.23.3 (Stan Hu)
-  - Fix bug where manually merged branches in a MR would end up with an empty diff (Stan Hu)
-  - Force update refs/merge-requests/X/head upon a push to the source branch of a merge request (Stan Hu)
   - Improved performance of finding users by one of their Email addresses
   - Improved performance of replacing references in comments
   - Show last project commit to default branch on project home page