HTTPResponse: produce fewer response headers

I am increasingly annoyed by how much non-essential work ZPublisher is doing, completely out of the control of the scrips ran by Zope. This is a small step in the direction of a bit fewer hard-coded non-essential behaviours, which should also go in the direction of satisfying more security audits criterion out-of-the-box. (still true, but now irrelevant to this merge request: it now only touches waitress configuration)

/cc @aurel @tatuya @jerome : please review in the context of the ongoing Zope4 porting efforts