DAOS-16677 doc: remove FQDN from docs & testcode

[osalyk]

Doc-only: true

Steps for the author:

• [x] Commit message follows the guidelines.
• [ ] Appropriate Features or Test-tag pragmas were used.
• [ ] Appropriate Functional Test Stages were run.
• [ ] At least two positive code reviews including at least one code owner from each category referenced in the PR.
• [ ] Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• [ ] Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions[bot]]

Ticket title is 'FQDN of internal test clusters mentioned in docs & testcode' Status is 'Open' Labels: 'scrubbed_2.8' https://daosio.atlassian.net/browse/DAOS-16677