Michal Terepeta authored Jan 26, 2018 and Ben Gamari committed Jan 26, 2018

Reasons to remove:
- It's confusing - we already have a widely used `Unique` module in
  `basicTypes/` that defines a newtype called `Unique`
- `Hoopl.Unique` is not actually used much

I've also moved the `Unique{Map,Set}` from `Hoopl.Unique` to
`Hoopl.Collections` to keep things together. But that module is also a
bit funny - it defines two type-classes that have only one instance
each. So we should probably either remove them or use them more
widely... In any case, that will be a separate change.

Signed-off-by: Michal Terepeta <michal.terepeta@gmail.com>

Test Plan: ./validate

Reviewers: bgamari, simonmar

Reviewed By: bgamari

Subscribers: kavon, rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4331