[Backport to 40] windowManager: Remove timeout on starting X11 services

With Xwayland started on demand, mutter/gnome-shell will spawn Xwayland and GNOME settings daemon Xsettings.

Currently, gnome-shell uses a timeout of 5 seconds before canceling the launch and declare failure to start X11 services.

While 5 seconds may seem like a lot of time, when this is executed on a virtual machine part of a QA tests under load, this causes random failures.

There is no good value here, we could increase the timeout but it will always remain racy. Instead, remove the timeout, systemd itself already has a timeout mechanism (with a much longer wait time).

Thanks to Benjamin Berg bberg@redhat.com for finding the root cause and suggesting the fix.

Part-of: !1888 (merged) (cherry picked from commit 8be5d336)