tidb: add warning message of drop table

[glorv]

What is changed, added or deleted? (Required)

Fix a wrong description of DROP TABLE IF EXISTS warning message. The origin related issue is resolved before v4.0.0.

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

• master (the latest development version)
• v6.6 (TiDB 6.6 versions)
• v6.5 (TiDB 6.5 versions)
• v6.4 (TiDB 6.4 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

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Do your changes match any of the following descriptions?

• 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:

• qiancai

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[qiancai]

@bb7133 Would you please help with the tech review? Thanks.

[qiancai]

/remove-status LGT1
/status LGT2

[qiancai]

/merge

[ti-chi-bot]

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

Commit hash: 5b6d315

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.4: #13597.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #13598.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.6: #13599.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #13601.