npm reverted to a backwards compatible cert

This PR removes the npm cert bugfix from two months ago.

From http://blog.npmjs.org/post/78165272245/more-help-with-self-signed-cert-in-chain-and-npm

> We are rolling back to the older cert now, but since the registry is distributed by a global CDN this process is slower than we’d like, and we don’t want to break things (further) by rushing the process.

@rockbot @ceejbot @izs @seldo it should be safe to remove this workaround by now, right?