chore: remove obsolete site content

[Conduitry]

These files are now outdated and unused - the canonical versions live in https://github.com/sveltejs/svelte.dev.

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[Conduitry]

I do want to note that when I mentioned this in Discord, @dominikg had some reservations about removing the examples and tutorial content, rather than backporting the changes and starting to sync those too. @dummdidumm was in favor of removing all of this. I'm not sure where I stand.

[dummdidumm]

IIRC we already agreed that tutorial/examples are only curated in the omnisite. Especially since the tutorial (and possibly at some point examples) don't just talk about Svelte, but also SvelteKit

[benmccann]

Presumably the kit tutorial would live in the kit repo if we wanted to sync them. I think there's a decent argument for that. It might encourage us to write tutorial content when adding new features. Otherwise I think we'll just continue to ignore the tutorial