With -XTypeInType, `*` must be imported to be used. This patch makes
sure the user knows this.

But I'm not sure this is the best way to deal with `*`. Feedback welcome
on either this small fix or the approach to `*`, in general.

You may wish to see `Note [HsAppsTy]` in HsTypes if you want to take a
broader view.

Test Plan: dependent/should_fail/RenamingStar

Reviewers: simonpj, bgamari, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1610