remove unnecessary usings

Author: Jasmine

src/GitHub.VisualStudio/Base/MenuBase.cs

@@ -6,9 +6,7 @@
 using System.Threading.Tasks;
 using GitHub.Api;
 using NullGuard;
-using GitHub.UI;
 using System.Diagnostics;
-using System.Linq;
 using GitHub.Primitives;
 
 namespace GitHub.VisualStudio

src/GitHub.VisualStudio/Menus/AddConnection.cs

@@ -4,7 +4,6 @@
 using GitHub.Services;
 using GitHub.UI;
 using GitHub.Extensions;
-using NullGuard;
 using GitHub.Api;
 
 namespace GitHub.VisualStudio.Menus

src/GitHub.VisualStudio/Menus/CopyLink.cs

@@ -5,7 +5,6 @@
 using GitHub.Extensions;
 using GitHub.Services;
 using GitHub.VisualStudio.UI;
-using NullGuard;
 using GitHub.Api;
 
 namespace GitHub.VisualStudio.Menus

src/GitHub.VisualStudio/Menus/OpenLink.cs

@@ -3,7 +3,6 @@
 using Microsoft.VisualStudio.Shell;
 using System;
 using System.ComponentModel.Composition;
-using NullGuard;
 using GitHub.Api;
 
 namespace GitHub.VisualStudio.Menus