Remove Note Siblings.

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

@@ -9,11 +9,5 @@ namespace osu.Game.Rulesets.Mania.Objects
     public abstract class ManiaHitObject : HitObject, IHasColumn
     {
         public int Column { get; set; }
-
-        /// <summary>
-        /// The number of other <see cref="ManiaHitObject"/> that start at
-        /// the same time as this hit object.
-        /// </summary>
-        public int Siblings { get; set; }
     }
 }