How to Hide the "WP Splash Image" Admin Menu

function plt_hide_wsi_menus() {
	//Hide the "Settings → WP Splash Image" menu.
	remove_submenu_page('options-general.php', 'wp_splash_image');
}

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

Where do I put this code?