Replace got for built-in fetch() API

[piranna]

Node.js v17.5.0 includes native support for fetch() API. Since Node.js v16 gets EOL in three months, it's safe to fully remove got dependency and use directly the built-in fetch() API. This reduces bundle size and also makes it almost dependencies-free except for the node-rsa dependency, that probably could be removed also by using the built-in crypto library, making the package fully dependencies-free also for the browser.