ddl: fix alter column drop default (#35072)

[ti-srebot]

cherry-pick #35072 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/35172

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git push git@github.com:ti-srebot/tidb.git pr/35172:release-5.0-cc46266e4a93

---

What problem does this PR solve?

Issue Number: close #35018

Problem Summary: fix alter column drop default

What is changed and how it works?

Check List

Tests

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

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.

fix `alter column drop default`

[ti-chi-bot]

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[ti-srebot]

/run-all-tests

[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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