How to Hide Manage Custom Notification Admin Menus

function plt_hide_manage_custom_notification_menus() {
	//Hide "Manage Custom Notification".
	remove_menu_page('category-list');
	//Hide "Manage Custom Notification → Categories".
	remove_submenu_page('category-list', 'category-list');
	//Hide "Manage Custom Notification → All Notifications".
	remove_submenu_page('category-list', 'notification-list');
	//Hide "Manage Custom Notification → Add New".
	remove_submenu_page('category-list', 'notification-insert');
}

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

Where do I put this code?