Made API models internal. Removed Discord.Net.API.

src/Discord.Net.Rest/API/Rest/GetReactionUsersParams.cs

@@ -0,0 +1,8 @@
+namespace Discord.API.Rest
+{
+    internal class GetReactionUsersParams
+    {
+        public Optional<int> Limit { get; set; }
+        public Optional<ulong> AfterUserId { get; set; }
+    }
+}