assistant2: Remove unneeded `#[allow(unused)]`s (#22979)

This PR removes some unneeded `#[allow(unused)]`s from the context types
in Assistant2.

We're using these fields now, so we no longer need to suppress the
unused lint.

Release Notes:

- N/A
2f07d53cceMarshall Bowers committed on 1/10/2025, 7:05:08 PM· committed by GitHubparentfe3d409
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