Removed `gen_answer`'s dead argument `question`

[jamesbraza]

The gen_answer tool has an unused question arg. This PR removes it.

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I observed for the LitQA2 question:

The gene EEF2 has introns 1 and 2, do they splice in a specific order?

The agent called gen_answer with the question arg:

Does the gene EEF2 splice intron 1 and 2 in a specific order?

Whereas this is mostly the same question, it has a few problems:

• The innards of gen_answer use state.session.question, not the input question, so the logs were inaccurate
• Perhaps the agent could cycle gen_answer with different input questions, when actually nothing different happens
• It not ideal to have learned agents learning this argument, when it's actually dead code
  • This also wastes both prompt and completion tokens