statistics: delete cluster status metrics on store deletion (#9945)

[ti-chi-bot]

This is an automated cherry-pick of #9945

What problem does this PR solve?

Issue Number: Close #9942

What is changed and how does it work?

Due to adding store label in #9898, we need to delete the related metrics on store deleting, otherwise it will retain forever.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

1. scale-in one tikv
2. pd-ctl store remove-tombstone

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

@okJiang This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

Details

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[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.80%. Comparing base (a91c005) to head (85be862).
⚠️ Report is 8 commits behind head on release-8.5.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-8.5   #10009   +/-   ##
============================================
  Coverage        77.79%   77.80%           
============================================
  Files              469      471    +2     
  Lines            63361    63459   +98     
============================================
+ Hits             49294    49376   +82     
- Misses           10435    10447   +12     
- Partials          3632     3636    +4     

Flag	Coverage Δ
unittests	77.80% <80.00%> (+<0.01%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bufferflies, okJiang

The full list of commands accepted by this bot can be found here.

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Details

Needs approval from an approver in each of these files:

• OWNERS [bufferflies]

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-15 01:45:09.460724413 +0000 UTC m=+1437454.274501975: ☑️ agreed by bufferflies.
• 2025-12-15 02:15:07.516429087 +0000 UTC m=+1439252.330206660: ☑️ agreed by okJiang.

[okJiang]

/unhold