This looks like some traces of an experiment to check if shadowing is good for
STG. The code refers to things that don't exist anymore and this part of
code hasn't been touched for ages, so I think this should be safe to
remove.

Test Plan: just comments

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: thomie, simonmar

Differential Revision: https://phabricator.haskell.org/D2114