tiflash: Remove the description about expr_blacklist in use_tiflash.md (#6891)

[ti-chi-bot]

This is an automated cherry-pick of #6891

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What is changed, added or deleted? (Required)

1. Remove the description about expr_blacklist in use_tiflash.md.
   we don't want users to open them.
2. remove the functions with bug.

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• master (the latest development version)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

@LittleFall @windtalker Please help resolve the conflict. Thanks!

[LittleFall]

LGTM

[ti-chi-bot]

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[TomShawn]

/merge

[ti-chi-bot]

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

Details

Commit hash: 3131038