Remove `programFindLocation` and `hookedPrograms` calls from Setup.hs

An upcoming version of the Cabal library will change the signature of the `programFindLocation` record field: <https://github.com/haskell/cabal/commit/84c4ddce652cd8f60c57c940abfbe927bb03654f#L7L49>

That change breaks this library's `Setup.hs`, which makes use of that record field. It looks to me like we can just remove the usage, which is much simpler than trying to use CPP to conditionally add a dummy argument.

The current `Setup.hs` checks for `pgconfig` and then `pg_config` on the path, and then uses that executable to find libpq's include/ and lib/ directories. To the best of my knowledge, `pgconfig` is not used by any recent version of PostgreSQL. (I've looked as far back as [version 7.2](http://www.postgresql.org/docs/7.2/static/app-pgconfig.html), released *12 years ago*.) Without needing that cascading path check, we can make do without the direct record field update.

I've also removed an unneeded use of the `hookedPrograms` record field in `main`. That made `pgconfig` available as a build tool to the .cabal file, which doesn't actually use it.