Sync: Allow importing / syncing templates

Purging a used template will obviously fail.

refs #11778

library/Director/Import/Sync.php

@@ -565,17 +565,6 @@ class Sync
             $modified = 0;
             $deleted = 0;
             foreach ($objects as $object) {
-                if ($object instanceof IcingaObject && $object->isTemplate()) {
-                    // TODO: allow to sync templates
-                    if ($object->hasBeenModified()) {
-                        throw new IcingaException(
-                            'Sync is not allowed to modify template "%s"',
-                            $object->object_name
-                        );
-                    }
-                    continue;
-                }
-
                 if ($object->shouldBeRemoved()) {
                     $object->delete($db);
                     $deleted++;