Remove Promise from interface.

src/Discord.Net.Core/Net/IRequest.cs

@@ -1,14 +1,10 @@
 using System;
-using System.IO;
-using System.Threading.Tasks;
 
 namespace Discord.Net
 {
     public interface IRequest
     {
         DateTimeOffset? TimeoutAt { get; }
-        TaskCompletionSource<Stream> Promise { get; }
         RequestOptions Options { get; }
-        
     }
 }