How to Hide Favicon by RealFaviconGenerator Admin Menus

function plt_hide_favicon_by_realfavicongenerator_menus() {
	//Hide the "Appearance → Favicon" menu.
	remove_submenu_page('themes.php', 'favicon-by-realfavicongenerator/admin/class-favicon-by-realfavicongenerator-admin.phpfavicon_appearance_menu');
	//Hide the "Settings → Favicon" menu.
	remove_submenu_page('options-general.php', 'favicon-by-realfavicongenerator/admin/class-favicon-by-realfavicongenerator-admin.phpfavicon_settings_menu');
}

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

Where do I put this code?