Revert change to render fallback when prerendering is disabled

[dimfeld]

Fixes #4492.

Loading hooks.js and/or executing the handle hook during the build process causes problems for some people, and so rendering the fallback page event when prerendering is disabled presents those people with build failures that can not be worked around. This PR reverts #4443, which enabled that behavior after the prerender process was moved into the build step.

For those like me who need a fallback page but are saddled with code that causes the build process to fail because Node.js throws a tantrum when you even try to import a page component, a configuration workaround is presented in the README for adapter-static. (An example is dependencies that are ESM compatible, but not in the exact one way that Node requires them to be.)

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🦋 Changeset detected

Latest commit: d3f059f

The changes in this PR will be included in the next version bump.

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@sveltejs/kit	Patch

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[Rich-Harris]

thank you!