remove unused import that breaks builds

Runtime/ChromeDevtools/DevtoolsProtocolHandler.cs

@@ -7,9 +7,7 @@ using Newtonsoft.Json.Linq;
 using System;
 using System.Collections;
 using System.Collections.Concurrent;
-using System.Collections.Generic;
 using System.Threading.Tasks;
-using UnityEditor.PackageManager;
 using UnityEngine;
 
 namespace bessw.Unity.WebView.ChromeDevTools