How to Hide the "Disk Usage Insights" Admin Menu

function plt_hide_disk_usage_insights_menus() {
	//Hide the "Tools → Disk Usage Insights" menu.
	remove_submenu_page('tools.php', 'disk-usage-insights');
}

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

Where do I put this code?