Remove duplicated entries from CHANGELOG

8.9.3 was consolidated with reworded CHANGELOG entries. This MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4890 had the CHANGELOG outdated re-introducing some duplicated entries when it was merged. This MR removes the duplicated ones.

Status changed to merged

mentioned in commit 7d8b6ac1

mentioned in issue #19488 (closed)

Removed ~149423 label