Update private data docs - remove SDK reference (backport #2770)

[mergify]

This is an automatic backport of pull request #2770 done by Mergify.
Cherry-pick of 52b12dc has failed:

On branch mergify/bp/release-2.2/pr-2770
Your branch is up to date with 'origin/release-2.2'.

You are currently cherry-picking commit 52b12dc47.
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Unmerged paths:
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	both modified:   docs/source/private-data-arch.rst

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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