Assign empty hit windows to HoldNoteBody

It's not a timed object, so following precedent, it should have empty
hitwindows.

This is not actually just aesthetics; several components check whether a
hitobject has empty hitwindows to determine whether to include it on
various HUD displays and results screen components where timed objects
are explicitly involved.

osu.Game.Rulesets.Mania/Objects/HoldNoteBody.cs

@@ -3,6 +3,7 @@
 
 using osu.Game.Rulesets.Judgements;
 using osu.Game.Rulesets.Mania.Judgements;
+using osu.Game.Rulesets.Scoring;
 
 namespace osu.Game.Rulesets.Mania.Objects
 {
@@ -15,5 +16,6 @@ namespace osu.Game.Rulesets.Mania.Objects
     public class HoldNoteBody : ManiaHitObject
     {
         public override Judgement CreateJudgement() => new HoldNoteBodyJudgement();
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }