In the config_defaults_inc.php, you can now set the delete_other_bug_threshold The comment of the field is wrong :

    /**
     * Access level needed to delete other users from the list of users
     * monitoring a bug.
     * Look in the constant_inc.php file if you want to set a different value.
     * @global int $g_monitor_add_others_bug_threshold
     */
    $g_monitor_delete_others_bug_threshold = DEVELOPER;

Should be :

    /**
     * Access level needed to delete other users from the list of users
     * monitoring a bug.
     * Look in the constant_inc.php file if you want to set a different value.
     * @global int $g_monitor_delete_others_bug_threshold
     */
    $g_monitor_delete_others_bug_threshold = DEVELOPER;