auth/rec web: stop sending Server: header

[zeha]

Short description

dnsdist does not, either. Avoids leaking VERSION to not authorized users.

Implements #4979.

Checklist

I have:

• [x] read the CONTRIBUTING.md document
• [x] compiled this code
• [x] tested this code
• [ ] included documentation (including possible behaviour changes)
• [ ] documented the code
• [ ] added or modified regression test(s)
• [ ] added or modified unit test(s)