Don't provide suggestions for certain global packages

[DanielRosenwasser]

If you have @types/node installed, you shouldn't get a completion item for node when typing import "n.

It's unclear what the right thing to do here is. I don't think you always want to filter out non-module packages because a package might just be written in a weird way where you import it and all it does is introduce globals. At the very least, we could do some quick-and-dirty filtering.