Fix build.

We don't need purgeResources public since it's part of the
ashmem internal optimization.

Change-Id: I65ba7545cf4801a8b97f3ece9b5ee5100c0f1c97

core/java/android/app/Notification.java

@@ -3797,6 +3797,9 @@ public class Notification implements Parcelable
             return wip;
         }
 
+        /**
+         * @hide
+         */
         public void purgeResources() {}
 
         // The following methods are split out so we can re-create notification partially.
@@ -3910,6 +3913,9 @@ public class Notification implements Parcelable
             return this;
         }
 
+        /**
+         * @hide
+         */
         @Override
         public void purgeResources() {
             super.purgeResources();