Drop get-proxy

[stevenvachon]

It doesn't support NO_PROXY and does not take an input URL (or protocol) to discern which env var to use, as there can be multiple. Meanwhile, proxy-from-env does all of this and more.

[stevenvachon]

I can write a PR for this, if you'd like; taking my tests from https://github.com/stevenvachon/auto-tunnel

The API would need to be changed to:

got('todomvc.com', {
	agent: caw('http://todomvc.com')
}, () => {});

…where the current first index (being a proxy URL override) would need to be changed to the request URL. This ties into #16