Wordpress: Remove Wordpress auto image height / width

gistfile1.php

// Removes the height & width that's automatically added
add_filter( 'post_thumbnail_html', 'remove_thumbnail_dimensions', 10 );
add_filter( 'image_send_to_editor', 'remove_thumbnail_dimensions', 10 );

function remove_thumbnail_dimensions( $html ) {
    $html = preg_replace( '/(width|height)=\"\d*\"\s/', "", $html );
    return $html;
}