test: de-flake rsc-cookies e2e tests (#71319)
Since the `/rsc-cookies-delete` path has a side effect (it runs a
middleware code path that deletes client cookies), prefetching this link
leads to unpredictable behaviours and possible failures in tests that
use this fixture, [such as this
one](https://github.com/vercel/next.js/blob/047baaba7d53326f157adc3aaf4b3fb3e13813c2/test/e2e/app-dir/app-middleware/app-middleware.test.ts#L126).
I fixed this with `prefetch={false}` but [per the
docs](https://nextjs.org/docs/pages/api-reference/components/link#prefetch)
it might be preferable to just use a plain `<a>` tag? I'm happy to make
that change if you prefer. Alternatively, maybe a `GET` shouldn't have
side effects; we could use a form here, fetch, or Server Action or
something instead.
Here's an example race when running the fixture manually (cookie 1 has
been unset by the `/rsc-cookies-delete` prefetch):
Co-authored-by: JJ Kasper <jj@jjsweb.site>
