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>