ci: drop stale tokenizers<0.23.0 override (#14504)

transformers now hard-requires tokenizers>=0.23.1,<0.24.0 at import time,
so the override from #13767 breaks every job at the environment step
(ImportError: tokenizers>=0.23.1,<0.24.0 is required ... found 0.22.2).
The originally-problematic 0.23.0 is already excluded by transformers'
own lower bound, so the override can go entirely.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>