server: Revert "server: Improve compatibility with MySQL 5.5 and 5.6 clients …

[djshow832]

…(#32338)"

This reverts commit 7e8ca4c.

What problem does this PR solve?

Issue Number: close #33141

Problem Summary:
Clients cannot connect to TiDB anymore.

What is changed and how it works?

Revert #32338 for now because it's safer.

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• bb7133
• tiancaiamao

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[bb7133]

LGTM

[tiancaiamao]

Maybe we need to add more ORM or other connector tests for such scenario...

[bb7133]

/merge

[ti-chi-bot]

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

Commit hash: 8573e0f

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/e73aef6d2c4bbd368925a2dc3b26bbc3c255b5ca