Squelch rollup warnings

[Rich-Harris]

Rollup is quite aggressive about warning on missing imports — if you have something this...

import * as foo from './foo.js';

if (foo.bar) {
  foo.bar();
}

...it will yell at you if foo.js doesn't export bar. This is a useful warning, unless the import is in code the user doesn't control, such as the generated app.js referencing client_hooks.handleError (which is known to be harmless).

This PR squelches those warnings.

---

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[changeset-bot]

🦋 Changeset detected

Latest commit: c8ec08e

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-13687-svelte.vercel.app/