Update CHANGELOG.md

Author: kraenhansen

packages/realm-react/CHANGELOG.md

@@ -1,16 +1,10 @@
 ## vNext (TBD)
 
-### Deprecations
-* None
-
-### Enhancements
-* None
-
-### Fixed
-* <How to hit and notice issue? what was the impact?> ([#????](https://github.com/realm/realm-js/issues/????), since v?.?.?)
-* None
+### Breaking changes
+* Removed all features related to [the deprecated](https://github.com/realm/realm-js/blob/main/DEPRECATION.md) Atlas Device Sync. ([PR-6879](https://github.com/realm/realm-js/pull/6879))
 
 ### Compatibility
+* Realm JS >= v20
 * React Native >= v0.71.4
 * Realm Studio v15.0.0.
 * File format: generates Realms with format v24 (reads and upgrades file format v10).