Modify the app Shell portion of tutorial doesn't need to have Shell.FlyoutBehavior="Disabled"

[PureWeen]

Issue description

We used to have this in our templates as well

But we've removed it because it isn't needed if you've specified "Tabbar". This can cause confusion when users try to switch to FlyoutItems because the flyout menu won't show up, so it's best to just leave it off :-)