perf(rspack_core): remove unnecessary `par_iter` from remove_parent_modules

[Boshen]

Summary

Creating parallel iterators on tight cpu loops with closer to cpu memory is useless here, removing these does not affect performance.

Related issue (if exists)

Types of changes

• [ ] Docs change / Dependency upgrade
• [ ] Bug fix
• [x] New feature / Improvement
• [ ] Refactoring
• [ ] Breaking change

Checklist

• [ ] I have added changeset via pnpm run changeset.
• [ ] I have added tests to cover my changes.

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 76ab1f91643bbfda867f4ae5ce11dbd5162d0dfd

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