borgbackup: use package from upstream NixOS service

mail-server/borgbackup.nix

@@ -16,7 +16,6 @@
 
 {
   config,
-  pkgs,
   lib,
   ...
 }:
@@ -67,15 +66,15 @@ let
   borgScript = ''
     export BORG_REPO=${repoLocation}
     ${cmdPreexec}
-    ${passphraseFragment} ${pkgs.borgbackup}/bin/borg init ${extraInitArgs} --encryption ${encryptionFragment} || true
-    ${passphraseFragment} ${pkgs.borgbackup}/bin/borg create ${extraCreateArgs} ${compression} ::${name} ${locations}
+    ${passphraseFragment} ${lib.getExe' config.services.borgbackup.package "borg"} init ${extraInitArgs} --encryption ${encryptionFragment} || true
+    ${passphraseFragment} ${lib.getExe' config.services.borgbackup.package "borg"} create ${extraCreateArgs} ${compression} ::${name} ${locations}
     ${cmdPostexec}
   '';
 in
 {
   config = lib.mkIf (config.mailserver.enable && cfg.enable) {
-    environment.systemPackages = with pkgs; [
-      borgbackup
+    environment.systemPackages = [
+      config.services.borgbackup.package
     ];
 
     systemd.services.borgbackup = {