remove unused code

Author: xiaoguzhu

Assets/Scripts/Core/Text/TextField.cs

@@ -34,7 +34,6 @@ public class TextField : DisplayObject, IMeshFactory
         float _fontSizeScale;
         float _renderScale;
         int _fontVersion;
-        Vector3 _lastPixelPerfectPos;
         string _parsedText;
 
         RichTextField _richTextField;