Add method to delete reaction with ids

src/Discord.Net.Rest/DiscordRestClient.cs

@@ -100,6 +100,9 @@ namespace Discord.Rest
         public Task<RestWebhook> GetWebhookAsync(ulong id, RequestOptions options = null)
             => ClientHelper.GetWebhookAsync(this, id, options);
 
+        public Task RemoveReactionAsync(ulong channelId, ulong messageId, ulong userId, IEmote emote, RequestOptions options = null)
+            => MessageHelper.RemoveReactionAsync(channelId, messageId, userId, emote, this, options);
+
         //IDiscordClient
         /// <inheritdoc />
         async Task<IApplication> IDiscordClient.GetApplicationInfoAsync(RequestOptions options)