xdg-autostart-generator: do not warn about unknown fields

xdg-autostart-generator: do not warn about unknown fields

My user manager says:
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.gnome.Terminal.desktop:256: Unknown key name 'Actions' in section 'Desktop Entry', ignoring.
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.gnome.Terminal.desktop:258: Unknown section 'Desktop Action new-window'. Ignoring.
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.gnome.Terminal.desktop:343: Unknown section 'Desktop Action preferences'. Ignoring.
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.telegram.desktop.desktop:12: Unknown key name 'Actions' in section 'Desktop Entry', ignoring.
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.telegram.desktop.desktop:13: Unknown key name 'SingleMainWindow' in section 'Desktop Entry', ignoring.
systemd-xdg-autostart-generator[2933]: /home/zbyszek/.config/autostart/org.telegram.desktop.desktop:19: Unknown section 'Desktop Action Quit'. Ignoring.

This is not useful. Those are externally-provided files, and they are likely to
have entries which we know nothing about.