Revert changes to make HitObject abstract

osu.Game/Rulesets/Objects/Legacy/ConvertHitObject.cs

@@ -0,0 +1,18 @@
+// 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.
+
+using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.Scoring;
+
+namespace osu.Game.Rulesets.Objects.Legacy
+{
+    /// <summary>
+    /// A hit object only used for conversion, not actual gameplay.
+    /// </summary>
+    internal abstract class ConvertHitObject : HitObject
+    {
+        public override Judgement CreateJudgement() => new IgnoreJudgement();
+
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
+    }
+}