ntp: make timesyncd the new default

- most nixos user only require time synchronisation,
  while ntpd implements a battery-included ntp server (1,215 LOCs of C-Code vs 64,302)
- timesyncd support ntp server per interface (if configured through dhcp for instance)
- timesyncd is already included in the systemd package, switching to it would
  save a little disk space (1,5M)

nixos/modules/virtualisation/google-compute-image.nix

@@ -125,7 +125,7 @@ in
     169.254.169.254 metadata.google.internal metadata
   '';
 
-  services.ntp.servers = [ "metadata.google.internal" ];
+  networking.timeServers = [ "metadata.google.internal" ];
 
   networking.usePredictableInterfaceNames = false;
 

nixos/modules/virtualisation/parallels-guest.nix

@@ -57,7 +57,7 @@ in
 
     boot.kernelModules = [ "prl_tg" "prl_eth" "prl_fs" "prl_fs_freeze" "acpi_memhotplug" ];
 
-    services.ntp.enable = false;
+    services.timesyncd.enable = false;
 
     systemd.services.prltoolsd = {
       description = "Parallels Tools' service";

nixos/modules/virtualisation/qemu-vm.nix

@@ -478,7 +478,7 @@ in
     boot.initrd.luks.devices = mkVMOverride {};
 
     # Don't run ntpd in the guest.  It should get the correct time from KVM.
-    services.ntp.enable = false;
+    services.timesyncd.enable = false;
 
     system.build.vm = pkgs.runCommand "nixos-vm" { preferLocalBuild = true; }
       ''

nixos/modules/virtualisation/xen-domU.nix

@@ -18,5 +18,5 @@
   services.syslogd.tty = "hvc0";
 
   # Don't run ntpd, since we should get the correct time from Dom0.
-  services.ntp.enable = false;
+  services.timesyncd.enable = false;
 }