How to Hide the "HTTP/2 Optimization" Admin Menu

function plt_hide_http2_optimization_menus() {
	//Hide the "Tools → HTTP/2 Optimization" menu.
	remove_submenu_page('tools.php', 'o10n-http2');
}

add_action('admin_menu', 'plt_hide_http2_optimization_menus', 51);

Where do I put this code?