Revert "Make all node packages available at the top level via their real name/version"

This makes attributes visible to nix-env that can't actually be
specified with -A, which is why there is a separate top-level in the
first place, duh.

This reverts commit ddb8b7f83136f64cff21adb3dcd300b742f4443f.

Signed-off-by: Shea Levy <shea@shealevy.com>