Issue #2151117 by Cottser, joelpittet: Remove theme_system_powered_by().

core/modules/system/lib/Drupal/system/Plugin/Block/SystemPoweredByBlock.php

@@ -25,7 +25,7 @@ class SystemPoweredByBlock extends BlockBase {
    * {@inheritdoc}
    */
   public function build() {
-    return array('#theme' => 'system_powered_by');
+    return array('#markup' => '<span>' . t('Powered by <a href="@poweredby">Drupal</a>', array('@poweredby' => 'http://drupal.org')) . '</span>');
   }
 
 }

core/modules/system/system.module

@@ -183,9 +183,6 @@ function system_theme() {
       'variables' => array('menu_items' => NULL),
       'file' => 'system.admin.inc',
     ),
-    'system_powered_by' => array(
-      'variables' => array(),
-    ),
     'system_compact_link' => array(
       'variables' => array(),
     ),
@@ -2739,15 +2736,6 @@ function system_time_zones($blank = NULL) {
   return $zones;
 }
 
-/**
- * Returns HTML for the Powered by Drupal text.
- *
- * @ingroup themeable
- */
-function theme_system_powered_by() {
-  return '<span>' . t('Powered by <a href="@poweredby">Drupal</a>', array('@poweredby' => 'http://drupal.org')) . '</span>';
-}
-
 /**
  * Returns HTML for a link to show or hide inline help descriptions.
  *