Clean up remaining bits related to ghc-cabal (#658)

Authored by snowleopard on Aug 26 2018, 8:46 AM.

Description

Clean up remaining bits related to ghc-cabal (Trac #658)

  • Drop ghcCabal package
  • Merge GhcCabal and CabalFlags builders
  • Use more consistent naming
  • Resolve import cycle
  • Rename parseCabal to parseCabalFile
  • Remove outdated references to ghc-cabal from comments