Use default:selection handler

Closes #2987189

src/Form/BanUserForm.php

@@ -41,9 +41,13 @@ class BanUserForm extends FormBase {
       '#type' => 'entity_autocomplete',
       '#target_type' => 'user',
       '#tags' => FALSE,
-      '#selection_handler' => 'private_message:not_blocked_user',
+      '#selection_handler' => 'default:user',
       '#selection_settings' => [
         'include_anonymous' => FALSE,
+        // @see \private_message_entity_query_user_alter()
+        'private_message' => [
+          'active_users_selection' => TRUE,
+        ],
       ],
     ];