Remove `.server`/`.client` module support

[markdalgleish]

Now that vite-env-only supports denyImports and denyFiles, we can remove this non-routing concern from our Vite plugin and allow consumers to control it separately. However, similar to vite-tsconfig-paths, I think we should provide a pre-configured usages of vite-env-only to any templates using our Vite plugin.

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Latest commit: bf200f71d544030235a15375b3775a2e694a0ea6

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[markdalgleish]

We've decided to maintain support for this, but we'll refactor to use vite-env-only internally.