refactor(batch): remove unused mem code

[chenzl25]

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What's changed and what's your intention?

• Remove the batch mem usage dead code introduced a long time ago without any progress.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added test labels as necessary. See details.
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• My PR contains breaking changes. (If it deprecates some features, please create a tracking issue to remove them in the future).
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• My PR changes performance-critical code. (Please run macro/micro-benchmarks and show the results.)

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Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

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