remove make-ghc-8.4.3

ghc build-depends on earlier versions of itself. In order to backport ghc-8.4.3 we'll also need to backport ghc.8.2.2. Since the versions are hard coded into the name of the helpers needed to do this, it takes manual maintenance to keep these helpers from breaking. In fact, this helper has been broken for Flidas since its release, so Flidas has the same version as Xenial. No one has complained or noticed in the year and a half since Flidas was released, so it doesn't seem like this package helper is worth the inconvenience of maintaining it.