ui: Don't set SetupWindow's visible property

When initializing a widget, the template is processed before the construct properties. That's usually fine, but showing a toplevel window has the side effect of realizing it; doing that before the window is associated with an application means that properties like the GTK application ID won't be exported, and gnome-shell fails to match the window to the correct .desktop file as a result.

Just remove the property from the template, the code already handles showingi the window.

See gnome-shell#2893