Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/action/action.api.php

@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * @file
+ * Hooks provided by the Actions module.
+ */
+
+/**
+ * Executes code after an action is deleted.
+ *
+ * @param $aid
+ *   The action ID.
+ */
+function hook_action_delete($aid) {
+  db_delete('actions_assignments')
+    ->condition('aid', $aid)
+    ->execute();
+}