Remove non-existing entries from Changelog

What does this MR do?

Based on the discussions in gitlab!85176 (comment 915050592) , we are moving 1.56.2, 1.54.2 and 1.51.2 release to the security release. We had included the changelogs for these releases pre-emptively in 1.57.0. This MR rectifies this discrepancy for 1.57.0 is released.

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines