diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index a7c8166a7506035a1a1c20a5f0176c1c690614c3..4140bbc14750f4cb8cc5826e9cb19794ff3862b4 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1096,23 +1096,6 @@ function template_preprocess_item_list(&$variables) {
   }
 }
 
-/**
- * Returns HTML for an indentation div; used for drag and drop tables.
- *
- * @param $variables
- *   An associative array containing:
- *   - size: Optional. The number of indentations to create.
- *
- * @ingroup themeable
- */
-function theme_indentation($variables) {
-  $output = '';
-  for ($n = 0; $n < $variables['size']; $n++) {
-    $output .= '<div class="js-indentation indentation">&nbsp;</div>';
-  }
-  return $output;
-}
-
 /**
  * Prepares variables for container templates.
  *
@@ -1779,7 +1762,6 @@ function drupal_common_theme() {
     ),
     'indentation' => array(
       'variables' => array('size' => 1),
-      'function' => 'theme_indentation',
     ),
     // From theme.maintenance.inc.
     'maintenance_page' => array(
diff --git a/core/modules/system/templates/indentation.html.twig b/core/modules/system/templates/indentation.html.twig
index e07e3c1c15e9b2bc4a45cd203f6b7814feee51e1..c7067fbe0843dfcaa5c9516836e6d5614e1dab09 100644
--- a/core/modules/system/templates/indentation.html.twig
+++ b/core/modules/system/templates/indentation.html.twig
@@ -11,10 +11,4 @@
  * @ingroup themeable
  */
 #}
-<!--
-THIS FILE IS NOT USED AND IS HERE AS A STARTING POINT FOR CUSTOMIZATION ONLY.
-See https://api.drupal.org/api/function/theme_indentation/8 for details.
-After copying this file to your theme's folder and customizing it, remove this
-HTML comment.
--->
 {% for i in 1..size if size > 0 %}<div class="js-indentation indentation">&nbsp;</div>{% endfor %}