statistics: mark NDV as deprecated and update variable scopes (#18318)#18321

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ti-chi-bot[bot] merged 2 commits intopingcap:release-8.0from ti-chi-bot:cherry-pick-18318-to-release-8.0

Aug 7, 2024

+2-2

Commits on Aug 7, 2024

This is an automated cherry-pick of pingcap#18318

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