planner: code refactoring for readability after AI test review

[mjonss]

What problem does this PR solve?

Issue Number: ref #49161

Problem Summary:
Some comments regarding the code was found after feeding the PR etc. into various LLMs as a test.

What changed and how does it work?

Should be less risk and easier to read.
Now also making use of slices.DeleteFunc which should be safer and better performance.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • Only refactoring, same old tests is enough

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ti-chi-bot]

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[tiprow]

Hi @mjonss. Thanks for your PR.

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[mjonss]

/retest

[mjonss]

/retest

[tiprow]

@mjonss: 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
fast_test_tiprow	055ca15	link	true	/test fast_test_tiprow

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[ti-chi-bot]

@mjonss: The following tests 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-tidb/check_dev	055ca15	link	true	/test check-dev
idc-jenkins-ci-tidb/check_dev_2	055ca15	link	true	/test check-dev2
idc-jenkins-ci-tidb/unit-test	055ca15	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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[ti-chi-bot]

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