Remove unused model

src/Discord.Net.Rest/API/Common/InteractionFollowupMessage.cs

@@ -1,20 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace Discord.API
-{
-    internal class InteractionFollowupMessage
-    {
-        public string Content { get; set; }
-        public Optional<string> Username { get; set; }
-        public Optional<string> AvatarUrl { get; set; }
-        public Optional<bool> TTS { get; set; }
-        public Optional<Stream> File { get; set; }
-        public Embed[] Embeds { get; set; }
-
-    }
-}