Deprocate in favor of phantomjs-prebuilt

[robrich]

Now that phantomjs-prebuilt (formerly phantomjs) includes phantomjs@2.1.1, do we need a separate phantomjs2 npm package?

[axelpale]

+1

If the package is not maintained anymore, devs please mention it on the top of the README. Just a line of text. If it would have saved me 30 minutes of work, then think the global impact.