How to Hide the "Scroll To CK" Admin Menu

function plt_hide_scroll_to_ck_menus() {
	//Hide the "Settings → Scroll To CK" menu.
	remove_submenu_page('options-general.php', 'scroll-to-ck');
}

add_action('admin_menu', 'plt_hide_scroll_to_ck_menus', 21);

Where do I put this code?