Reverting some accidentally ressurected CHANGELOG entries (#3768)

## Motivation and Context
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## Description
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## Testing
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## Checklist
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rather than leaving it unchecked -->
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

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