Remove redundant dependency on com.unity.ugui.

Author: timbotimbo

example/unity/DemoApp/Assets/FlutterUnityIntegration/Demo/Scripts/Rotate.cs

@@ -1,10 +1,9 @@
 using System;
 using FlutterUnityIntegration;
 using UnityEngine;
-using UnityEngine.EventSystems;
 using System.Globalization;
 
-public class Rotate : MonoBehaviour, IEventSystemHandler
+public class Rotate : MonoBehaviour
 {
     [SerializeField]
     Vector3 RotateAmount;