Add missing release note

Issue: #7902
PiperOrigin-RevId: 331771187

RELEASENOTES.md

@@ -254,6 +254,9 @@
         to `DownloadManager.Listener.onDownloadChanged`.
     *   Support multiple non-overlapping write locks for the same key in
         `SimpleCache`.
+    *   Remove `CacheUtil`. Equivalent functionality is provided by a new
+        `CacheWriter` class, `Cache.getCachedBytes`, `Cache.removeResource` and
+        `CacheKeyFactory.DEFAULT`.
 *   DRM:
     *   Remove previously deprecated APIs to inject `DrmSessionManager` into
         `Renderer` instances. `DrmSessionManager` must now be injected into