windows/cygwin-setup: Drop meta.platforms attr.

This prevents cross-builds, so let's drop it for now.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/os-specific/windows/cygwin-setup/default.nix

@@ -42,6 +42,5 @@ stdenv.mkDerivation rec {
     homepage = https://sourceware.org/cygwin-apps/setup.html;
     description = "A tool for installing Cygwin";
     license = licenses.gpl2Plus;
-    platforms = platforms.cygwin;
   };
 }