Remove old 1.x auth stack (#4485)

* Remove old 1.x auth stack

Fixes dotnet/aspnetcore#3999

Author: HaoK

Messages/RequestToken.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNetCore.Http.Authentication;
-
 namespace Microsoft.AspNetCore.Authentication.Twitter
 {
     /// <summary>

Messages/RequestTokenSerializer.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.IO;
-using Microsoft.AspNetCore.Http.Authentication;
 
 namespace Microsoft.AspNetCore.Authentication.Twitter
 {

TwitterEvents.cs

@@ -35,7 +35,7 @@ public class TwitterEvents : RemoteAuthenticationEvents
         /// <summary>
         /// Called when a Challenge causes a redirect to authorize endpoint in the Twitter handler
         /// </summary>
-        /// <param name="context">Contains redirect URI and <see cref="Http.Authentication.AuthenticationProperties"/> of the challenge </param>
+        /// <param name="context">Contains redirect URI and <see cref="AuthenticationProperties"/> of the challenge </param>
         public virtual Task RedirectToAuthorizationEndpoint(RedirectContext<TwitterOptions> context) => OnRedirectToAuthorizationEndpoint(context);
     }
 }