lint: Discord Namespace Clean-up (#1185)

* Remove RpcException

* Move RestConnection to Discord.Net.Rest

* Remove RpcVirtualMessageChannel

* Move REST objects to Discord.Net.Rest

* Fix Discord.Rest namespace

src/Discord.Net.Core/Net/RpcException.cs

@@ -1,17 +0,0 @@
-using System;
-
-namespace Discord
-{
-    public class RpcException : Exception
-    {
-        public int ErrorCode { get; }
-        public string Reason { get; }
-
-        public RpcException(int errorCode, string reason = null)
-            : base($"The server sent error {errorCode}{(reason != null ? $": \"{reason}\"" : "")}")
-        {
-            ErrorCode = errorCode;
-            Reason = reason;
-        }
-    }
-}