YARN-5920. Fix deadlock in TestRMHA.testTransitionedToStandbyShouldNotHang. Contributed by Varun Saxena.

(cherry picked from commit e15c20edba1e9a23475ee6a4dfbadbdb8c1f668a)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/TestRMHA.java

@@ -463,8 +463,7 @@ public class TestRMHA {
 
     MemoryRMStateStore memStore = new MemoryRMStateStore() {
       @Override
-      public synchronized void updateApplicationState(
-          ApplicationStateData appState) {
+      public void updateApplicationState(ApplicationStateData appState) {
         notifyStoreOperationFailed(new StoreFencedException());
       }
     };