chore: remove mentions of sonnet 3.5

[sydney-runkle]

see https://docs.claude.com/en/docs/about-claude/model-deprecations#2025-08-13%3A-claude-sonnet-3-5-models

[codspeed-hq]

CodSpeed Performance Report

Merging #33737 will not alter performance

_{Comparing sr/no-more-sonnet-3-5 (e65666c) with master (28564ef)¹}

Summary

✅ 3 untouched
⏩ 31 skipped²

Footnotes

1. No successful run was found on master (ac58d75) during the generation of this report, so 28564ef was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 31 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. ↩