Disable system env generator to work around selinux denials
    
    The system env generator is used to get the list of flatpak apps in
    gnome-initial-setup for parental controls support. We don't have
    parental controls enabled in F33 and F34 (although it's planned for
    F35), so we can just disable the system env generator to work around the
    selinux denials for now while we don't have the selinux policy side
    changes figured out.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1947214
    https://bugzilla.redhat.com/show_bug.cgi?id=1916652
    https://github.com/flatpak/flatpak/issues/4128