Remove user_categories since they've been removed in Backdrop
As per https://www.drupal.org/node/1393236 the category system was removed from user view and edit (before Backdrop forked). Full conversation here: https://www.drupal.org/node/1291100
As per https://www.drupal.org/node/1393236 the category system was removed from user view and edit (before Backdrop forked). Full conversation here: https://www.drupal.org/node/1291100