chrony: disable the whole timesyncd module when chronyd is enabled

Peviously only the timesyncd systemd unit was disabled. This meant
that when you activate a system that has chronyd enabled the following
strange startup behaviour takes place:

  systemd[1]: Starting chrony NTP daemon...
  systemd[1]: Stopping Network Time Synchronization...
  systemd[1]: Stopped chrony NTP daemon.
  systemd[1]: Starting Network Time Synchronization...