gnu: Remove Haskell packages provided by GHC.

* gnu/packages/haskell.scm (ghc-array, ghc-binary, ghc-bytestring,
ghc-directory, ghc-haskeline, ghc-process, ghc-transformers,
ghc-transformers-0.4.2.0): Remove.
(ghc-tar)[inputs]: Remove ghc-array.
(ghc-hslogger)[inputs]: Remove ghc-directory.
* gnu/packages/version-control.scm (darcs)[inputs]: Remove ghc-array,
ghc-binary, and ghc-haskeline.
* gnu/packages/wm.scm (xmonad)[inputs]: Remove ghc-directory.

Signed-off-by: Ricardo Wurmus <rekado@elephly.net>