nixos/bluetooth: fix restartIfChanged

X-RestartIfChanged must be in the Service section, not in Unit and we also have a shortcut for that.

https://github.com/NixOS/nixpkgs/blob/8cc0451ead532078052ac7d3aa82e23572047acf/nixos/lib/systemd-lib.nix#L796

nixos/modules/services/hardware/bluetooth.nix

@@ -143,6 +143,8 @@ in
           {
             wantedBy = [ "bluetooth.target" ];
             aliases = [ "dbus-org.bluez.service" ];
+            # restarting can leave people without a mouse/keyboard
+            restartIfChanged = false;
             serviceConfig = {
               ExecStart = [
                 ""
@@ -171,8 +173,6 @@ in
 
               PrivateNetwork = false; # tethering
             };
-            # restarting can leave people without a mouse/keyboard
-            unitConfig.X-RestartIfChanged = false;
           };
       }
       // (optionalAttrs cfg.hsphfpd.enable {