Remove "use strict" directives in tests

We set alwaysStrict so this directive is not needed

src/vs/workbench/services/configuration/test/electron-browser/configurationEditingService.test.ts

@@ -3,8 +3,6 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-'use strict';
-
 import * as sinon from 'sinon';
 import * as assert from 'assert';
 import * as os from 'os';