WordPress adds meta tags for shortlink, RSD (Really Simple Discovery), and wlwmanifest (Windows Live Writer). Most sites do not need them. Add to your functions.php file. For more on securing WordPress.
remove_action( 'wp_head', 'wp_shortlink_wp_head' );
remove_action( 'wp_head', 'rsd_link' );
remove_action( 'wp_head', 'wlwmanifest_link' );
remove_action( 'wp_head', 'wp_generator' );