ghcjs: revert "mark build as broken"

This reverts commit 8f07d4bd78. The build
failure blocking this package has been fixed in the meanwhile. Thanks to
@basvandijk for the heads-up.

pkgs/development/compilers/ghcjs/default.nix

@@ -176,5 +176,4 @@ in mkDerivation (rec {
   license = stdenv.lib.licenses.bsd3;
   platforms = ghc.meta.platforms;
   maintainers = with stdenv.lib.maintainers; [ jwiegley cstrahan ];
-  broken = true;   # See http://hydra.nixos.org/build/41499439, for example.
 })