xdg-autostart: Ignore all files with GNOME autostart phase

xdg-autostart: Ignore all files with GNOME autostart phase

If an autostart file for GNOME has a phase specified, then this implies
it is a session service that needs to be started at a specific time.

We have no way of handling the ordering, and while it does make sense
to explicitly hide these services with X-systemd-skip, there is no point
in even trying to handle them.