Redirect to home page without using deprecated methods
Try using Url::fromInternalUri then instead of fromUri():

https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Url.php/function/Url%3A%3AfromInternalUri/8.2.x

It specifically notes the use of front and none. But you can't pass the URL object or path tokens to RedirectResponse, as this is a Drupal construct. That class expects the following arguments:

http://api.symfony.com/2.3/Symfony/Component/HttpFoundation/RedirectResponse.html

string  $url        The URL to redirect to
integer $status     The response status code
array   $headers    An array of response headers


$url needs to be a string, so on your URL object, call ->toString() to get the URL.

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Url.php/function/Url%3A%3AtoString/8.2.x