fix: clear usings

Lytvynenko-Danylo · Lytvynenko-Danylo · commit 9683be8bf6fc · 2020-10-07T15:13:04.000+03:00
diff --git a/com.stansassets.plugins-dev-kit/Editor/UIToolkit/DocumentationTab/DocumentationTab.cs b/com.stansassets.plugins-dev-kit/Editor/UIToolkit/DocumentationTab/DocumentationTab.cs
@@ -4,7 +4,6 @@
 using StansAssets.Foundation.UIElements;
 using UnityEditor.SceneManagement;
 using UnityEngine;
-using UnityEngine.Serialization;
 using UnityEngine.UIElements;
 
 #if UNITY_2019_4_OR_NEWER
