config: remove defaultTraceRegionFlow (#8009)

[ti-chi-bot]

This is an automated cherry-pick of #8009

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]

This pull request has been approved by:

• rleungx

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[ti-chi-bot]

@ti-chi-bot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci/build	78a9a96	link	true	/test build

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[lhy1024]

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