YGNodeInit is no longer exported

Summary:
- Problem: Can't link yoga static libraries with Unity and Xamarin.iOS since YGNodeInit is undefined in the libraries.
- Solution: Remove the reference in Native.cs

Reviewed By: emilsjolander

Differential Revision: D4338485

fbshipit-source-id: 9dc95aec8f1fd50f3f9d66e1623afe2fb1992210

csharp/Facebook.Yoga/Native.cs

@@ -27,9 +27,6 @@ namespace Facebook.Yoga
         [DllImport(DllName)]
         public static extern IntPtr YGNodeNew();
 
-        [DllImport(DllName)]
-        public static extern void YGNodeInit(IntPtr node);
-
         [DllImport(DllName)]
         public static extern void YGNodeFree(IntPtr node);