chore: remove some unused mocks

[Rich-Harris]

follow-up to #16813 (comment)

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 19f96d5:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/19f96d56ecbd91fa5f3dd6dee10206cf336aedff

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16841

[changeset-bot]

⚠️ No Changeset found

Latest commit: 19f96d5

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.

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16841-svelte.vercel.app/

[teemingc]

Nice