Removes old note about named imports in ESM

[fox1t]

As of today, you can import the named Fastify import in the ESM context with no issues.

Namely, this works as expected:

import { fastify } from "fastify";

const app = fastify({
  logger: true,
});

await app.listen({ port: 3000 });

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[github-actions]

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