Remove ensure_single_line co-location

app/assets/javascripts/locale/es6/ensure_single_line.js

-// co-locating ensure_single_line to satisfy static analysis while allowing Node.js to import the function with CommonJS
-
-import ensureSingleLine from '../ensure_single_line';
-
-export default ensureSingleLine;

app/assets/javascripts/locale/index.js

 import Jed from 'jed';
-import ensureSingleLine from './es6/ensure_single_line';
+import ensureSingleLine from './ensure_single_line';
 import sprintf from './sprintf';
 
 const languageCode = () => document.querySelector('html').getAttribute('lang') || 'en';

spec/frontend/locale/ensure_single_line_spec.js

-import ensureSingleLine from '~/locale/es6/ensure_single_line';
+import ensureSingleLine from '~/locale/ensure_single_line';
 
 describe('locale', () => {
   describe('ensureSingleLine', () => {