How to Hide Newsletter Admin Menus

function plt_hide_newsletter_menus() {
	//Hide "Newsletter".
	remove_menu_page('newsletter_main_index');
	//Hide "Newsletter → Dashboard".
	remove_submenu_page('newsletter_main_index', 'newsletter_main_index');
	//Hide "Newsletter → Welcome".
	remove_submenu_page('newsletter_main_index', 'newsletter_main_welcome');
	//Hide "Newsletter → Settings and More".
	remove_submenu_page('newsletter_main_index', 'newsletter_main_main');
	//Hide "Newsletter → List building".
	remove_submenu_page('newsletter_main_index', 'newsletter_subscription_options');
	//Hide "Newsletter → Security".
	remove_submenu_page('newsletter_main_index', 'newsletter_subscription_antibot');
	//Hide "Newsletter → Newsletters".
	remove_submenu_page('newsletter_main_index', 'newsletter_emails_index');
	//Hide "Newsletter → Subscribers".
	remove_submenu_page('newsletter_main_index', 'newsletter_users_index');
	//Hide "Newsletter → Addons".
	remove_submenu_page('newsletter_main_index', 'newsletter_main_extensions');
}

add_action('admin_menu', 'plt_hide_newsletter_menus', 91);

Where do I put this code?