Merge branch '12366-gfm-autocomplete' into 'master'

Removes EE differences for gfm_autocomplete

Closes #12366

See merge request gitlab-org/gitlab-ee!14343

app/assets/javascripts/gfm_auto_complete.js

 import $ from 'jquery';
 import 'at.js';
 import _ from 'underscore';
-
 import glRegexp from './lib/utils/regexp';
 import AjaxCache from './lib/utils/ajax_cache';