nixos/tests: remove icewm taskbar (#456757)

  services.displayManager.defaultSession = lib.mkDefault "none+icewm";

  services.xserver.windowManager.icewm.enable = true;

  environment.etc = {

    # Help with OCR

  environment.etc."icewm/theme".text = ''

    "icewm/theme".text = ''

      Theme="gtk2/default.theme"

    '';

    # Remove task bar to avoid non-determinism

    "icewm/preferences".text = ''

      ShowTaskBar=0

    '';

  };

}