How to Hide Dr. Flex Admin Menus

function plt_hide_dr_flex_menus() {
	//Hide "Dr. Flex".
	remove_menu_page('drflex_plugin_settings');
	//Hide "Dr. Flex → Configuration".
	remove_submenu_page('drflex_plugin_settings', 'drflex_plugin_settings');
	//Hide "Dr. Flex → Button integration".
	remove_submenu_page('drflex_plugin_settings', 'drflex_plugin_settings_integration');
	//Hide "Dr. Flex → Code examples".
	remove_submenu_page('drflex_plugin_settings', 'drflex_plugin_settings_examples');
}

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

Where do I put this code?