display: move gdm_display_get_timed_login_details to manager
    
    The function is no longer virtualized among the display types,
    and it doesn't actually have a full picture of whether or not the
    display should do automatic/timed login so move it up to the manager,
    where all the information is.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746492