Fix up release build

Author: h3xds1nz

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Data/RBTree.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -664,8 +664,10 @@ public void LoadTree(string s)
         private string _savedTree;
 
 #else
-        void Verify(int expectedSize, bool checkSort = true) { }
-        void SaveTree() { }
+        private void Verify(int expectedSize, bool checkSort = true) { }
+
+        private void SaveTree() { }
+
         public void LoadTree(string s) { }
 #endif // DEBUG
         #endregion Debugging