Prevent overlogging of debug msgs in Graph impl

* Refactored the logging in Graph to honour the 
Levels set in Logger.
* Got rid of some un-used methods.

testng-core/src/main/java/org/testng/internal/Graph.java

@@ -21,7 +21,6 @@
  * @author Cedric Beust, Aug 19, 2004
  */
 public class Graph<T> {
-  private static final boolean m_verbose = true;
   private final Map<T, Node<T>> m_nodes = Maps.newLinkedHashMap();
   private List<T> m_strictlySortedNodes = null;
   private final Comparator<Node<T>> comparator;
@@ -59,7 +58,6 @@ public void addPredecessor(T tm, T predecessor) {
       throw new TestNGException("Non-existing node: " + tm);
     } else {
       node.addPredecessor(predecessor);
-      addNeighbor(tm, predecessor);
       // Remove these two nodes from the independent list
       initializeIndependentNodes();
       m_independentNodes.remove(predecessor);
@@ -68,10 +66,6 @@ public void addPredecessor(T tm, T predecessor) {
     }
   }
 
-  private void addNeighbor(T tm, T predecessor) {
-    findNode(tm).addNeighbor(findNode(predecessor));
-  }
-
   private Collection<Node<T>> getNodes() {
     return m_nodes.values();
   }
@@ -133,9 +127,7 @@ public void topologicalSort() {
     }
 
     log("=============== DONE SORTING");
-    if (m_verbose) {
-      dumpSortedNodes();
-    }
+    dumpSortedNodes();
   }
 
   private void initializeIndependentNodes() {
@@ -173,15 +165,11 @@ private void removeFromNodes(List<Node<T>> nodes, Node<T> node) {
   }
 
   private static void log(String s) {
-    if (m_verbose) {
-      Logger.getLogger(Graph.class).debug("[Graph] " + s);
-    }
+    log(() -> s);
   }
 
   private static void log(Supplier<String> s) {
-    if (m_verbose) {
-      Logger.getLogger(Graph.class).debug("[Graph] " + s.get());
-    }
+    Logger.getLogger(Graph.class).debug("[Graph] " + s.get());
   }
 
   private Node<T> findNodeWithNoPredecessors(List<Node<T>> nodes) {
@@ -253,12 +241,6 @@ public Node(T tm) {
       m_object = tm;
     }
 
-    private final Set<Node<T>> m_neighbors = new HashSet<>();
-
-    public void addNeighbor(Node<T> neighbor) {
-      m_neighbors.add(neighbor);
-    }
-
     @Override
     public Node<T> clone() {
       Node<T> result = new Node<>(m_object);