Remove width and height attributes from [gallery] output

WordPress automatically adds the width and height attributes to shortcode images.

How to delete these attributes? Something like this but for output.

I can think of a couple of options:

1. Create a new shortcode, e.g. my_gallery. You can copy the code in
   wp-includes/media.php. Look for the code staring with
   add_shortcode('gallery', 'gallery_shortcode'); and then the actual
   function. Rename / modify as needed. The actual img link is within
   the $link variable

2. Use something like this (untested), which should work but might
   strip-out all width/height from any link.

_

add_filter('wp_get_attachment_link', 'remove_img_width_height', 10, 1);

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