chore: remove some unnecessary code

[Rich-Harris]

follow-up to #16150. While merging main into the async branch I realised that I messed up the condition here — we only want to schedule effects that are dirty, not the ones that are clean. But it turns out they're already scheduled, and this code is completely unnecessary.

We do still need it on the async branch, but not here

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[changeset-bot]

⚠️ No Changeset found

Latest commit: 3916877

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-16160-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16160