How to Hide the "Staging Colours" Admin Menu

function plt_hide_set_admin_colour_on_staging_and_dev_menus() {
	//Hide the "Settings → Staging Colours" menu.
	remove_submenu_page('options-general.php', 'set-admin-colour-on-staging-and-dev');
}

add_action('admin_menu', 'plt_hide_set_admin_colour_on_staging_and_dev_menus', 1000000000);

Where do I put this code?