Delete Redundant RoutingServiceTests (#37750)

* This test compleletly overrode the `reroute` method and hence did nothing put test the override itself
   * Removed the test since it tests nothing and simplified `reroute` accordingly

Author: original-brownbear

server/src/main/java/org/elasticsearch/cluster/routing/RoutingService.java

@@ -77,11 +77,6 @@ protected void doClose() {
      * Initiates a reroute.
      */
     public final void reroute(String reason) {
-        performReroute(reason);
-    }
-
-    // visible for testing
-    protected void performReroute(String reason) {
         try {
             if (lifecycle.stopped()) {
                 return;