Revert "Use consistent package naming for HEAD.nix files" for GHC and GHCjs.

This reverts commit 31b0e34d1dd1226de1492101e3aeea60292196d7. The version
numbers used in that commit were no improvement.

pkgs/development/compilers/ghc/head.nix

···
 
   commonBuildInputs = [ ghc perl autoconf automake happy alex python3 ];
 
-  version = "2017-01-06";
+  version = "8.1.20170106";
   rev = "b4f2afe70ddbd0576b4eba3f82ba1ddc52e9b3bd";
 
   commonPreConfigure =  ''
···
   '';
 in stdenv.mkDerivation (rec {
   inherit version rev;
-  name = "ghc-unstable-${version}";
+  name = "ghc-${version}";
 
   src = fetchgit {
     url = "git://git.haskell.org/ghc.git";

pkgs/development/compilers/ghcjs/head.nix

···
 { fetchgit, fetchFromGitHub, bootPkgs }:
 
 bootPkgs.callPackage ./base.nix {
-  version = "2017-03-23";
+  version = "0.2.020170323";
 
   inherit bootPkgs;