Removing activeNode as it is not used

Author: StanleyGoldman

src/UnityExtension/Assets/Editor/GitHub.Unity/UI/TreeControl.cs

@@ -29,7 +29,6 @@ public abstract class Tree: ITree
 
         [SerializeField] private List<TreeNode> nodes = new List<TreeNode>();
         [SerializeField] private TreeNode selectedNode = null;
-        [SerializeField] private TreeNode activeNode = null;
         [SerializeField] private TreeNodeDictionary folders = new TreeNodeDictionary();
 
         [NonSerialized] private Stack<bool> indents = new Stack<bool>();
@@ -99,11 +98,6 @@ public void AddNode(string path, string label, int level, bool isFolder, bool is
             SetNodeIcon(node);
             nodes.Add(node);
 
-            if (isActive)
-            {
-                activeNode = node;
-            }
-
             if (isSelected)
             {
                 SelectedNode = node;