Add back removed xmldoc

osu.Game/Skinning/LegacySkinTransformer.cs

@@ -8,6 +8,9 @@
 
 namespace osu.Game.Skinning
 {
+    /// <summary>
+    /// Transformer used to handle support of legacy features for individual rulesets.
+    /// </summary>
     public abstract class LegacySkinTransformer : SkinTransformer
     {
         /// <summary>

osu.Game/Skinning/Skin.cs

@@ -25,7 +25,7 @@
 
 namespace osu.Game.Skinning
 {
-    public abstract partial class Skin : IDisposable, ISkin
+    public abstract class Skin : IDisposable, ISkin
     {
         private readonly IStorageResourceProvider? resources;