fix(nuxt): don't stub out unenv

[danielroe]

Description

In preparation for upcoming h3 1.8.0 release, this removes the unenv stub that we currently have in histoire. There may be some extra context I'm unaware of though in #443 for why this is present. (I'm hoping the underlying reason has been addressed/resolved upstream since then.)

I'm including h3-nightly in deps to confirm (in CI) that this resolves the underlying issue; I'll remove before marking ready to merge.

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• Bug fix
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