bench: remove some duplication

[sylvestre]

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #8816 will degrade performances by 100%

_{Comparing sylvestre:bench-dedup (c25f303) with main (443c201)[^unexpected-base]} [^unexpected-base]: No successful run was found on main (5b261bc) during the generation of this report, so 443c201 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report.

Summary

❌ 1 regression
✅ 126 untouched
⏩ 6 skipped[^skipped]

:warning: Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	b64_encode_synthetic	164.4 µs	11,352,357.3 µs	-100%
[^skipped]: 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports.

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Congrats! The gnu test tests/du/files0-from is no longer failing!