X-Delivered-to header now left on forwarded email

When forwarding email, we would remove all the normal headers we add to delivered email (eg X-Mail-from, X-Delivered-to, X-Resolved-to, X-Spam-hits, X-Spam-score) for privacy reasons. Several people noted that X-Delivered-to is actually quite useful on forwarded email when you have multiple different aliases or virtual domains. We have now changes our configuration so that X-Delivered-to is now left in the headers of forwarded email, the other headers are still removed