In Windows Phone 8.1 XAML App , the Status Bar has been included which provides the similar functionality of the SystemTray from Windows Phone 8 app. The users can hide the Status Bar in Windows Phone 8.1 App via code as shown below.

How to hide Status Bar in Windows Phone 8.1 App ?

StatusBar sBar = Windows.UI.ViewManagement.StatusBar.GetForCurrentView();
await sBar.HideAsync();