Should be enough to just remove jetpack.css

remove-jetpack-css.php

<?php
/*
MU Plugin: remove-jetpack-css
Plugin Name: WP Remove jetpack.css
Plugin URI: http://required.ch
Description: Removes the jetpack.css
Version: 1.0
Author: Silvan Hagen
Author URI: http://www.silvanhagen.com
License: GPLv3
*/

// Remove the concatinated jetpack.css
function remove_jetpack_styles() {
  wp_deregister_style( 'jetpack-css' ); // Concatinated jetpack.css
}
add_action('wp_print_styles', 'remove_jetpack_styles' );
?>