Fixed visual bug when deleting last timer/world clock

I propose to remove the transition between the list of world clocks and world clock status page and the transition between the list of timer and the timer's "Select duration" page. Because there is a visual bug that happens every time where the ListBox doesn't have any children so it collapses, leaving an ugly shadow.

I think it shouldn't look out of place because there isn't already any transition between the World, Alarm, Stopwatch and Timer page.