nixosTests.flatpak: clean up

GNOME is not necessary. Portals probably are not either,
but the NixOS module requires them.

Not sure why it did not work without GNOME before.

Changed files
+1 -4
nixos
tests
installed-tests
+1 -4
nixos/tests/installed-tests/flatpak.nix
···
withX11 = true;
testConfig = {
-
services.xserver.desktopManager.gnome3.enable = true; # TODO: figure out minimal environment where the tests work
-
# common/x11.nix enables the auto display manager (lightdm)
-
services.xserver.displayManager.gdm.enable = false;
-
services.gnome3.core-utilities.enable = false;
+
xdg.portal.enable = true;
services.flatpak.enable = true;
environment.systemPackages = with pkgs; [ gnupg ostree python3 ];
virtualisation.memorySize = 2047;