[RFC 55] Remove package net/http from stdlib

[mfelsche]

The net/http package has already been moved to https://github.com/ponylang/http so it can be safely removed
from the stdlib to execute RFC 55.

HTTP examples have also been removed.

[SeanTAllen]

@mfelsche can you add release notes for this to PR before its merged as this is a breaking change.

[mfelsche]

Release notes draft

The net/http package has been removed from the stdlib, with it the HTTPClient, HTTPServer and URL classes. They now live in the http package and can be included using stable by adding them to your bundle.json like so:

stable add github ponylang/http --tag 0.1.0

The code in the new repository at version 0.1.0 is exactly the same as it was when it was removed from stdlib. Thus the only change you need to do is to change your imports from use "net/http" to use "http".