remove unused DiscoveryNodes#valid method

core/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java

@@ -77,14 +77,6 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
         return nodes.valuesIt();
     }
 
-    /**
-     * Is this a valid nodes that has the minimal information set. The minimal set is defined
-     * by the localNodeId being set.
-     */
-    public boolean valid() {
-        return localNodeId != null;
-    }
-
     /**
      * Returns <tt>true</tt> if the local node is the elected master node.
      */