haskell-jailbreak-cabal: clean up overrides

pkgs/development/haskell-modules/configuration-common.nix

···
   hackage-security = dontCheck super.hackage-security;
 
   # Link statically to avoid runtime dependency on GHC.
-  jailbreak-cabal = (disableSharedExecutables super.jailbreak-cabal).override { Cabal = self.Cabal_1_20_0_4; };
+  jailbreak-cabal = disableSharedExecutables super.jailbreak-cabal;
 
   # enable using a local hoogle with extra packagages in the database
   # nix-shell -p "haskellPackages.hoogleLocal { packages = with haskellPackages; [ mtl lens ]; }"

pkgs/development/haskell-modules/configuration-ghc-8.0.x.nix

···
   unix = null;
   xhtml = null;
 
-  # jailbreak-cabal can use the native Cabal library.
-  jailbreak-cabal = super.jailbreak-cabal.override { Cabal = null; };
-
   # https://github.com/bmillwood/applicative-quoters/issues/6
   applicative-quoters = appendPatch super.applicative-quoters (pkgs.fetchpatch {
     url = "https://patch-diff.githubusercontent.com/raw/bmillwood/applicative-quoters/pull/7.patch";