fixup! tests: Add stack-simple

Author: rvl

test/stack-simple/stack-pkgs.nix

@@ -1,11 +1,5 @@
 {
   overlay = hackage:
-    { packages = {} // { stack-simple = ./.stack.nix/stack-simple.nix; };
-
-      # fixme: there was no compiler attribute generated by stack-to-nix
-      compiler.version = "8.6.2";
-      compiler.nix-name = "ghc862";
-    };
+    { packages = {} // { stack-simple = ./.stack.nix/stack-simple.nix; }; };
   resolver = "lts-13.6";
-  compiler = "ghc-8.6.2";
-}
+  }