Krzysztof Gogolewski authored Feb 17, 2020 and Marge Bot committed Feb 24, 2020

* Remove outdated Note [HsForAllTy tyvar binders] and [Context quantification].
  Since the wildcard refactor 1e041b73, HsForAllTy no longer has an flag
  controlling explicity. The field `hsq_implicit` is gone too.
  The current situation is covered by Note [HsType binders] which is already
  linked from LHsQTyVars.
* Small refactor in CoreLint, extracting common code to a function
* Remove "not so sure about WpFun" in TcEvidence, per Richard's comment
  ghc/ghc!852 (comment 223226)
* Use mkIfThenElse in Foreign/Call, as it does exactly what we need.