Core: rm Setup.hs as it becomes deprecated and puzles HLS

The HLS had problem that it was detecting the cabal.project in root of our
monorepo, but also was founding the Setup.hs that promised that it is a simple
project structure. And was trying to run the Core with `runhaskell`.

So HLS was throwing several errors. The explicit definition of cradles allowed
HLS to understand that it is a monorepo. And the removement of Setup.hs is
because it is not recommended anymore, and upstream work plans to deprecate it
completely in favour of arriving proper solution.