[fix] remove vestigial JSON server_data

[Conduitry]

When we started serializing server data with devalue, the old JSON serialization of it was left in. This removes it.

This also updates the types so that server_data is no longer a valid type to pass to render_json_payload_script. This required a slight adjustment to the unit tests.

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🦋 Changeset detected

Latest commit: 8c571ee

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[Conduitry]

The difference with and without the extra server_data block can be seen on, for example https://kit.svelte.dev/docs/introduction and https://kit-svelte-di38rlap3-svelte.vercel.app/docs/introduction

[Rich-Harris]

JFC these windows test timeouts are killing me. wtf is wrong with github actions