Remove unneeded using directives

Author: fubar-coder

RestSharp.Portable.Test/AuthenticationTests.cs

@@ -1,15 +1,11 @@
 using System;
-using System.Configuration;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Net;
-using System.Security.Cryptography;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 
-using Org.BouncyCastle.Crypto;
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.OpenSsl;