**breaking:** remove YGNodeGetInstanceCount

Summary:
@public

`YGNodeGetInstanceCount` was only ever meant for tests, and caused data races in multi-threaded environments.

It was completely replaced with event-based counting for tests.

Here we remove public API around the counter, and the counter itself.

Reviewed By: SidharthGuglani

Differential Revision: D15174857

fbshipit-source-id: 228e85da565bac9e8485121e956a2e41910b11c8

csharp/Facebook.Yoga/YogaNode.cs

@@ -673,10 +673,5 @@ namespace Facebook.Yoga
             return _children != null ? ((IEnumerable<YogaNode>)_children).GetEnumerator() :
                 System.Linq.Enumerable.Empty<YogaNode>().GetEnumerator();
         }
-
-        public static int GetInstanceCount()
-        {
-            return Native.YGNodeGetInstanceCount();
-        }
     }
 }