How to exclude a function from executing on AMP pages in Wordpress?

Question

Accelerated Mobile Pages

How to exclude a function from executing on AMP pages in Wordpress?

if (!(is_admin() && is_amp_endpoint())) {
    function defer_parsing_of_js ( $url ) {
        if ( FALSE === strpos( $url, '.js' ) ) return $url;
        if ( strpos( $url, 'jquery.js' ) ) return $url;
        return "$url defer=\"defer\"";
    }
    add_filter( 'clean_url', 'defer_parsing_of_js', 11, 1 );
}

Why does this code work on AMP pages? How to fix it?