Fix slider tail evaluation in osu difficulty calculator

The slider tail circle was already included as a nested hit object and is judged before the end of the slider's actual duration, so using the slider end time leads to an inaccurate travel distance and end position.

osu.Game.Rulesets.Osu/Difficulty/Preprocessing/OsuDifficultyHitObject.cs

@@ -143,7 +143,6 @@ private void computeSliderCursorPosition(Slider slider)
             var scoringTimes = slider.NestedHitObjects.Skip(1).Select(t => t.StartTime);
             foreach (var time in scoringTimes)
                 computeVertex(time);
-            computeVertex(slider.EndTime);
         }
 
         private Vector2 getEndCursorPosition(OsuHitObject hitObject)