qrencode: depend on libiconv unconditionally

libiconv is already defined per-platform.  The actual libiconv library
won't be built on platforms like Linux where it doesn't need to be, so
there's no need to maintain a separate platform list here.

Required to build for FreeBSD.

pkgs/development/libraries/qrencode/default.nix

@@ -13,8 +13,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ pkg-config ];
 
-  buildInputs = [ libpng ]
-    ++ lib.optionals stdenv.isDarwin [ libiconv libobjc ];
+  buildInputs = [ libiconv libpng ]
+    ++ lib.optionals stdenv.isDarwin [ libobjc ];
 
   configureFlags = [
     "--with-tests"