Coding standards

Fixes issue introduced in 38f3ef3a.

src/Plugin/CKEditorPlugin/MathJaxPlugin.php

@@ -3,7 +3,6 @@
 namespace Drupal\uw_cfg_common\Plugin\CKEditorPlugin;
 
 use Drupal\ckeditor\CKEditorPluginBase;
-use Drupal\Core\File\FileSystem;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\editor\Entity\Editor;
 use Drupal\Core\Asset\LibrariesDirectoryFileFinder;