Hide `Data.OldList` module

Summary:
The `Data.OldList` module was originally created in
3daf0023 to provide a way to access the
original list-specialised functions from `Data.List`. It was also made
an exposed module in order to facilitate adapting the
`haskell2010`/`haskell98` packages. However, since the
`haskell2010`/`haskell98` packages were dropped, we no longer need to
expose `Data.OldList`.

Depends on D511

Reviewers: ekmett, austin

Reviewed By: ekmett, austin

Subscribers: thomie, carter

Differential Revision: https://phabricator.haskell.org/D513