Removed unnecessary TextField override

no issue
- Ember's TextSupport mixin (used by TextField and TextArea) has had `autofocus` as an `attributeBinding` since 1.5.0 so the override to add it is not necessary

ghost/admin/app/app.js

@@ -1,6 +1,5 @@
 import 'ghost-admin/utils/link-component';
 import 'ghost-admin/utils/route';
-import 'ghost-admin/utils/text-field';
 import Application from '@ember/application';
 import Resolver from './resolver';
 import config from './config/environment';

ghost/admin/app/utils/text-field.js

@@ -1,5 +0,0 @@
-import TextField from '@ember/component/text-field';
-
-TextField.reopen({
-    attributeBindings: ['autofocus']
-});