nixos/perlless: remove redundant `system.switch.enableNg`

{

  # switch-to-configuration-ng reimplements switch-to-configuration, but

  # without perl.

  system.switch = lib.mkDefault {

    enable = false;

    enableNg = true;

  };

  # Remove perl from activation

  boot.initrd.systemd.enable = lib.mkDefault true;

  system.etc.overlay.enable = lib.mkDefault true;