The definition of `setUnfoldingInfoLazily` is exactly the same as
`setUnfoldingInfo` and is only used in one place, `TcIface`.

They were made equivalent in 2010 in
2ff2497d with the commit message.

{{{
commit 2ff2497d
Author: Ian Lynagh <igloo@earth.li>  Wed Oct 20 15:37:10 2010
Committer:      Ian Lynagh <igloo@earth.li>  Wed Oct 20 15:37:10 2010
Original File:  compiler/basicTypes/IdInfo.lhs

Don't seq unfoldings
We generate intermediate unfoldings which are just thrown away, so
evaluating them is a waste of time.
}}}

Closes #12453