Explicitly remove Transfer-Encoding header from 204 and 304 responses

Per RFC 2616 §10.3.6 & §10.2.5 (http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html) "The [204/304] response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields."