Update census and sentiment examples to only use Keras, and remove estimator usage, since estimator is deprecated in TF 2.16.

PiperOrigin-RevId: 609376031

Author: zoyahav

RELEASE.md

@@ -14,6 +14,8 @@
 *   Added python 3.11 support.
 *   Depends on `tensorflow>=2.15.0,<3`.
 *   Enable passing `tf.saved_model.SaveOptions` to model saving functionality.
+*   Census and sentiment examples updated to only use Keras instead of
+    estimator.
 
 ## Breaking Changes