Fatal error: Call to undefined method CI_Session::sess_destroy() 1.7.2

My current version of ci is 1.7.2 but ehen i am using

            $this->session->unset_userdata('uid');
            $this->session->unset_userdata('email');
            $this->session->sess_destroy();

in my controller an below shown is my class controller

      function Account()
{
    parent::BEV_Controller();   
    $this->load->model('facebook_model');
    $this->load->library('session');
    $this->form_validation->set_error_delimiters('<div class="error">', '</div>');
}