Removed superfluous benefits relation fetch
Removed superfluous benefits relation fetch

refs https://github.com/TryGhost/Team/issues/919

As we pass the `benefits` to the Product model on creation, we do not
need to manually fetch them again. In fact doing so causes a strange SQL
error, where we attempt to run `SELECT undefined.*`.

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost