How to have a "classic" book menu toc ?

Hello
On book pages, the book toc is rendered as an "Outline" menu.
I would get back to the classic behavior (no menu, only the sibling nodes).
Should i rebuild the default behavior and override the theme or is there a simple way to achieve my goal ?

edit : here is what i have done to remove the "outline" menu :

// in sites/all/themes/mytheme/template.php
function mytheme_theme_registry_alter(&$theme_registry) {
  $key = array_search('bootstrap_process_book_navigation', $theme_registry['book_navigation']['process functions']);
  if ($key !== FALSE) {
    unset($theme_registry['book_navigation']['process functions'][$key]);
  }
}