Transports like websocket include Jetty Server header with its version.
The is a flag to disable it, available in etc/jetty.xml but it works just for the web console.
There's no way to set it on HTTP-based transports that create a Jetty server by itself.

 HTTP/1.1 302 Found
 Location: http://localhost:8181/hawtio
 Content-Length: 0
 Server: Jetty(9.2.23.v20171218)