chore: remove handlebars

[Uzlopak]

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

[jsumners]

Is there a reason?

[Uzlopak]

@jsumners

the handlebars test does not make any sense, and is more like a handlebars test than a fastify-static test.

[gurgunday]

I get the test part but the example without a template engine is dangerous as if a file name contains " or a special HTML char, the template in this example would break

Even if it would be fine here, it's not a good practice to show it as an example I think

[Uzlopak]

Maybe, but even we are not using handlebars in our implementation of fastifystatic

[mcollina]

lgtm