disable the watchdog by default
The systemd watchdog has three big problems:
- it wrongly restarts KWin in some cases after suspend
- it wrongly restarts KWin in some OOM situations
- it wrongly restarts KWin when doing a live upgrade from the watchdog being disabled to it being enabled
Each of those cases can cause users to lose data and in the upgrade case even require repairing the system manually, which is not acceptable. This commit keeps the watchdog code in place for now; the decision to remove it or what to replace it with isn't as urgent.