Remove unused import.

src/Renci.SshNet.Tests/Classes/Messages/Transport/KeyExchangeDhGroupExchangeReplyBuilder.cs

@@ -1,5 +1,4 @@
-using System.Collections.Generic;
-using System.Text;
+using System.Text;
 using Renci.SshNet.Common;
 using Renci.SshNet.Messages.Transport;