Remove (undocumented) advanced flag in details config output

[DL6ER]

What does this implement/fix?

As suggested by @yubiuser in pi-hole/web#2882 (comment)

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
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• I have read the above and my PR is ready for review.

[rdwebdesign]

This flag is used in web#2882:

https://github.com/pi-hole/web/blob/99c85fc1709bcc8e3d1f8e3b4da58d3e9de05edb/scripts/pi-hole/js/settings.js#L42

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[DL6ER]

Rebased on latest development-v6

[github-actions]

Conflicts have been resolved.