Remove unused classes and replace overlay in game

osu.Game/Overlays/BeatmapListing/SortCriteria.cs

@@ -0,0 +1,17 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+namespace osu.Game.Overlays.BeatmapListing
+{
+    public enum SortCriteria
+    {
+        Title,
+        Artist,
+        Difficulty,
+        Ranked,
+        Rating,
+        Plays,
+        Favourites,
+        Relevance
+    }
+}