Avoid updating hitobjects unnecessarily for start time changes

This was firing regardless of whether the start time was changed, such
as where beat snap provided the same time the object already has.

The case where a change actually occurs is already handled by
EditorBeatmap (see `startTimeBindables`), so it turns out this local
handling is not required at all.

osu.Game/Screens/Edit/Compose/Components/BlueprintContainer.cs

@@ -496,10 +496,7 @@ namespace osu.Game.Screens.Edit.Compose.Components
                 double offset = result.Time.Value - movementBlueprints.First().HitObject.StartTime;
 
                 foreach (HitObject obj in Beatmap.SelectedHitObjects)
-                {
                     obj.StartTime += offset;
-                    Beatmap.Update(obj);
-                }
             }
 
             return true;