CHANGELOG: add decommissioned flags

To update the changelog with the deprecated flags that re decommissioned in v3.6.

Signed-off-by: Niket1997 <[email protected]>

Author: Niket1997

CHANGELOG/CHANGELOG-3.6.md

@@ -26,7 +26,6 @@ Previous change logs can be found at [CHANGELOG-3.5](https://github.com/etcd-io/
 
 ### Removed Deprecated Flags
 In this release, we have removed several flags that were available in etcd 3.5. These flags were previously marked as deprecated and are now fully decommissioned in 3.6. The removed flags are as follows:
-
 - `--enable-v2`
 - `--experimental-enable-v2v3`
 - `--proxy`