Update release notes

- Remove SampleQueue changes (they're being picked up in 2.12, but
  are sufficiently minor to not warrant a release note)
- Update 2.12 estimated release date

PiperOrigin-RevId: 330409443

RELEASENOTES.md

@@ -2,14 +2,10 @@
 
 ### dev-v2 (not yet released)
 
-*   Core library:
-    *   Add `SampleQueue.discardUpstreamFrom` so upstream samples can be
-        discarded by timestamp.
-    *   Add `SampleQueue.getLargestReadTimestampUs`.
 *   Track selection:
     *   Add option to specify multiple preferred audio or text languages.
 
-### 2.12.0 (not yet released - targeted for 2020-09-03) ###
+### 2.12.0 (not yet released - targeted for 2020-09-11) ###
 
 *   Core library:
     *   `Player`: