release.nix: remove firefox-unwrapped from darwin-tested

Unfortunately it is broken and I won’t have time to fix right now.
Most likely we will have to wait until the macOS 10.12 update to get
this one working again.

pkgs/top-level/release.nix

@@ -62,7 +62,7 @@ let
               jobs.vim.x86_64-darwin
 
               # UI apps
-              jobs.firefox-unwrapped.x86_64-darwin
+              # jobs.firefox-unwrapped.x86_64-darwin
               jobs.qt5.qtmultimedia.x86_64-darwin
               jobs.inkscape.x86_64-darwin
               jobs.gimp.x86_64-darwin