fix: remove unnecessary tslib dependency

[fcrozatier]

tslib was added to the Svelte codebase in sveltejs/svelte#920 but the --importHelpers option since disappeared from the tsconfig during the split in sveltejs/svelte#2994. This option as well as downlevelling are also not set by create-svelte.

So this library is unused, and there is no need to keep it. This PR removes it.

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🦋 Changeset detected

Latest commit: 45d57f0

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

This PR includes changesets to release 1 package

Name	Type
create-svelte	Patch

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[dummdidumm]

Thanks! @benmccann I noticed that the create-vite template also have the dependency needlessly, I think we can remove it there, too