This was a poorly typed attempt to mimic TypeScript's index signatures,
which we can use instead.
This eliminates a very strange type that we were exposing to users, but
not re-exporting through our public API.
Fixes#4483
BREAKING CHANGE:
This change moves the http module into angular2/, so its import
path is now angular2/http instead of http/http.
Many other modules have also been moved around inside of angular2,
but the public API paths have not changed as of this commit.