Switch stack's Cabal build from Custom back to Simple

Split out of #2450. Right now (after #2223) we need a Custom build to possibly store in stack the list of dependencies it was built with. But @mgsloan explains that

> Setup.hs files are generally gnarly for a variety of reasons - haskell/cabal#3065

EDIT: The idea would be to switch to Template Haskell for the job, ideas in
https://github.com/commercialhaskell/stack/issues/2450#issuecomment-238108150 and pointers.