update latin1 as an alias for utf8mb4

[Defined2014]

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• This PR is translated from:
• Other reference link(s): *: Support modify table/column charset from latin1 to utf8/utf8mb4 tidb#34386

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• Delete files
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[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn
• tangenta

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[TomShawn]

The related code has been reverted and there is no release plan for this feature.