I faced the same problem and finally ending by using the wpcf7_form_elements
filter to remove the <span>
tag with a regex. You can for example copy-paste this code in your functions.php
file. Here I pass an an anonymous function as a callback, so be sure to have PHP >= 5.3.
add_filter('wpcf7_form_elements', function($content) {
$content = preg_replace('/<(span).*?class="\s*(?:.*\s)?wpcf7-form-control-wrap(?:\s[^"]+)?\s*"[^\>]*>(.*)<\/\1>/i', '\2', $content);
return $content;
});