statistics: delete cluster status metrics on store deletion

[okJiang]

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.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.67%. Comparing base (4a11b99) to head (05d7b94).
⚠️ Report is 80 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9945      +/-   ##
==========================================
+ Coverage   78.65%   78.67%   +0.02%     
==========================================
  Files         495      495              
  Lines       66469    66475       +6     
==========================================
+ Hits        52279    52301      +22     
+ Misses      10398    10387      -11     
+ Partials     3792     3787       -5     

Flag	Coverage Δ
unittests	78.67% <100.00%> (+0.02%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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,rleungx]

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

[LGTM Timeline notifier]

Timeline:

• 2025-11-21 08:09:30.042565038 +0000 UTC m=+258333.691759495: ☑️ agreed by rleungx.
• 2025-11-21 08:10:47.950726763 +0000 UTC m=+258411.599921220: ☑️ agreed by bufferflies.

[okJiang]

/retest

[okJiang]

/retest

[okJiang]

/retest

[ti-chi-bot]

@bufferflies: You cannot manually add or delete the cherry pick branch category labels. It will be added automatically by bot when the PR is created.

Details

In response to adding label named type/cherry-pick-for-release-8.5.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #10009.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #10188.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #10189.
But this PR has conflicts, please resolve them!