Removed unnecessary using statement

Author: JeremyCaney

OnTopic.Editor.AspNetCore/Models/EditingTopicViewModel.cs

@@ -6,7 +6,6 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Diagnostics.CodeAnalysis;
 using OnTopic.Editor.AspNetCore.Models.Metadata;
 using OnTopic.Mapping.Annotations;
 using OnTopic.Metadata;