alert: remove keep_alive_total metric

[hfxsd]

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• This PR is translated from:alert: remove keep_alive_total metric docs-cn#18227
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• Delete files
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-02 07:57:38.806571311 +0000 UTC m=+76256.025332914: ☑️ agreed by qiancai.

[hfxsd]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #18448.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #18449.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.0: #18450.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #18451.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.2: #18452.