Remove WIN_STRUCT macro

If ARM compatibility still requires the WIN_STRUCT macro, we have a lot of additional changes to make. Removing for now, as this is clearly broken for some Yoga values (e.g., margin, padding, etc.). Will follow up with another PR after validating that we still need to pass structs by ref in RS1 or later.

csharp/Facebook.Yoga/YogaValue.cs

@@ -91,17 +91,5 @@ namespace Facebook.Yoga
         {
             return Point(pointValue);
         }
-
-#if WINDOWS_UWP_ARM
-        internal static YogaValue MarshalValue(IntPtr ptr)
-        {
-            return Marshal.PtrToStructure<YogaValue>(ptr);
-        }
-#else
-        internal static YogaValue MarshalValue(YogaValue value)
-        {
-            return value;
-        }
-#endif
     }
 }