How to Hide Really Simple SSL Admin Menus

function plt_hide_really_simple_ssl_menus() {
	//Hide the "Settings2 → SSL2" menu.
	remove_submenu_page('options-general.php', 'really-simple-security');
}

add_action('admin_menu', 'plt_hide_really_simple_ssl_menus', 11);

Where do I put this code?