Remove superfluous validation of incoming states

This commit removes a superfluous check when validing incoming cluster
states. The check in question prevents out-of-order cluster states from
the same master from entering the queue. However, such out-of-order
cluster states will be cleaned from the queue when a commit message for
that cluster state arrives or a commit message for any higher-versioned
cluster state arrives.

core/src/main/java/org/elasticsearch/discovery/zen/publish/PublishClusterStateAction.java

@@ -419,20 +419,6 @@ public class PublishClusterStateAction extends AbstractComponent {
             throw new IllegalStateException(message);
         }
 
-        if (lastSeenClusterState != null && lastSeenClusterState.supersedes(incomingState)) {
-            final String message = String.format(
-                    Locale.ROOT,
-                    "received cluster state from current master superseded by last seen cluster state; " +
-                            "received version [%d] with uuid [%s], last seen version [%d] with uuid [%s]",
-                    incomingState.version(),
-                    incomingState.stateUUID(),
-                    lastSeenClusterState.version(),
-                    lastSeenClusterState.stateUUID()
-            );
-            logger.warn(message);
-            throw new IllegalStateException(message);
-        }
-
     }
 
     protected void handleCommitRequest(CommitClusterStateRequest request, final TransportChannel channel) {