fix: drop stale language-hint caveats in Qwen3 ASR

[kapitalismho]

Summary

• Fixes parts of the Qwen3-ASR docs that don't match how the models actually behave.
• Qwen3-ASR 0.6B and 1.7B have accepted language hints since ccc2db0, but the docs still say an explicit hint can't be set.

Scope

• Docs and comments only. I kept this to the minimal fix of removing the stale parts.
• After merging, the HF card descriptions will need to be updated as well.

AI Assistance

• The work was done with help from Claude Opus 5.5. I reviewed the diff myself.

Validation

• Ran qwen3_asr_e2e_smoke and transcribe-cli against 0.6B (Q8_0) and 1.7B (Q4_K_M). Matching --language hints give the same transcript as auto-detect, invalid codes return
  UNSUPPORTED_LANGUAGE, and batching works.
• The catalog CI steps pass locally, including render.py --check and generate.py for both cards.

[cjpais]

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