config: remove defaultTraceRegionFlow

[JmPotato]

What problem does this PR solve?

Issue Number: ref #7917.

What is changed and how does it work?

Remove unused `defaultTraceRegionFlow`.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• rleungx

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[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 26cbbb6

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against tikv/pd#release-6.5 from head ti-chi-bot:cherry-pick-8009-to-release-6.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"No commits between tikv:release-6.5 and ti-chi-bot:cherry-pick-8009-to-release-6.5"}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against tikv/pd#release-6.5 from head ti-chi-bot:cherry-pick-8009-to-release-6.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"No commits between tikv:release-6.5 and ti-chi-bot:cherry-pick-8009-to-release-6.5"}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #8065.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #8145.