backup: add a dummy removePrivateFields

src/backups.js

@@ -11,6 +11,8 @@ exports = module.exports = {
     list,
     del,
 
+    removePrivateFields,
+
     BACKUP_IDENTIFIER_BOX: 'box',
     BACKUP_IDENTIFIER_MAIL: 'mail',
 
@@ -52,6 +54,10 @@ function postProcess(result) {
     return result;
 }
 
+function removePrivateFields(backup) {
+    return backup;
+}
+
 async function add(data) {
     assert(data && typeof data === 'object');
     assert.strictEqual(typeof data.remotePath, 'string');