use fs.rmdir recursive

This...
https://github.com/bcoe/c8/blob/a465b65d907b669714cfc3dca949efd667f499c3/bin/c8.js#L32
could possible be replaced by:
```js
await fs.fsPromises.rmdir(argv.tempDirectory, { recursive: true })
```

if not now, then maybe in the feature when you decide to drop support for < 12.10

(only looking into all my sub dependencies seeing if there is anyway to reduce the total size)