Remove unused code for now

I don't think we'll ever be using this anyway.

osu.Game/Rulesets/Objects/HitObject.cs

@@ -1,11 +1,9 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using System.Collections.Generic;
 using osu.Game.Audio;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.ControlPoints;
-using osu.Game.Rulesets.Judgements;
 using osu.Game.Rulesets.Objects.Types;
 
 namespace osu.Game.Rulesets.Objects
@@ -32,10 +30,6 @@ namespace osu.Game.Rulesets.Objects
         /// </summary>
         public SampleInfoList Samples = new SampleInfoList();
 
-        public virtual IEnumerable<Judgement> CreateJudgements() => new[] { new Judgement() };
-
-        public readonly List<HitObject> Children = new List<HitObject>();
-
         /// <summary>
         /// Whether this <see cref="HitObject"/> is in Kiai time.
         /// </summary>