[docs] remove outdated note

[dominikg]

vite-plugin-svelte has prebundleSvelteLibraries enabled by default now

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• [ ] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• [ ] This message body should clearly illustrate what problems it solves.
• [ ] Ideally, include a test that fails without this PR but passes with it.

Tests

• [ ] Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• [ ] If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. All changesets should be patch until SvelteKit 1.0

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 9453b69434c2deb23acb54634d5bf262c35e5801

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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Click here to learn what changesets are, and how to add one.

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[vercel[bot]]

@dominikg is attempting to deploy a commit to the Svelte Team on Vercel.

A member of the Team first needs to authorize it.

[Rich-Harris]

Pretty sure this can be closed, since the same change was applied in #8327