chore: remove explicit env var flag from service workers

[Rich-Harris]

this was needed in v2, but we no longer use this flag

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 953b8dc:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/953b8dc8465622273f67a0270c779fd5a401375d

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16433

[changeset-bot]

⚠️ No Changeset found

Latest commit: 953b8dc

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

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

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

Click here if you're a maintainer who wants to add a changeset to this PR

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16433-svelte.vercel.app/