TEST: Remove legacy reduction concurrency smoke test

[vyasr]

Description

Removes an undocumented 2019 concurrency smoke test for Series reductions. It had no result assertions or linked regression history; ordinary reduction correctness remains covered by the existing test matrix.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between e78c254 and 83efd3d.

📒 Files selected for processing (1)

• python/cudf/cudf/tests/series/methods/test_reductions.py

💤 Files with no reviewable changes (1)

• python/cudf/cudf/tests/series/methods/test_reductions.py

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📝 Summary

Summary by CodeRabbit

• Tests
  • Removed an unused import and a concurrent series-reduction test.
  • Existing reduction test coverage remains unchanged.

Walkthrough

Changes

Reduction test cleanup

Layer / File(s)	Summary
Remove thread-pool test coverage python/cudf/cudf/tests/series/methods/test_reductions.py	Removed the unused ThreadPoolExecutor import and the concurrent series-reduction test. Other reduction tests remain unchanged.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 83efd

This cleanup removes obsolete test code without changing production behavior or established reduction correctness coverage. The change is mergeable.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description accurately explains the removal of the legacy concurrency smoke test and states that existing reduction coverage remains unchanged.
Title check	✅ Passed	The title clearly identifies the test change and matches the pull request's primary objective.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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