Fix onComplete assignment.

src/Avalonia.Animation/Animation.cs

@@ -85,12 +85,7 @@ namespace Avalonia.Animation
         /// Sets the behavior for having a delay between repeats for this animation.
         /// </summary>
         public bool DelayBetweenRepeats { get; set; }
-        
-        public Animation()
-        {
-            this.CollectionChanged += delegate { _isChildrenChanged = true; };
-        }
-  
+
         private (IList<IAnimator> Animators, IList<IDisposable> subscriptions) InterpretKeyframes(Animatable control)
         {
             var handlerList = new List<(Type type, AvaloniaProperty property)>();

src/Avalonia.Animation/AnimatorStateMachine`1.cs

@@ -73,7 +73,7 @@ namespace Avalonia.Animation
 
             animationDirection = animation.PlaybackDirection;
             fillMode = animation.FillMode; 
-            onComplete = onComplete;
+            this.onComplete = onComplete;
         }
 
         public void Step(PlayState playState, long frameTick, Func<double, T, T> Interpolator)