[remove] unnecessary member

Author: Garume

Assets/ContextCircleMenu/Editor/Core/CircleMenus/CircleMenu.cs

@@ -16,7 +16,6 @@ public abstract class CircleMenu
 
         private bool _alreadyInitialized;
         private IButtonFactory _buttonFactory;
-        private VisualElement _preparedElement;
 
         protected CircleButton[] ButtonElements;
         protected VisualElement[] UtilityElements;