python3.pkgs.keyutils: fix cross

When cross-compiling, tests aren't run, and check inputs aren't
available.  But pytest-runner was a setup requirement, so keyutils
would fail to build without it, even though we weren't running the
tests.  To fix that, drop the pytest-runner setup requirement.

pkgs/development/python-modules/keyutils/default.nix

@@ -12,6 +12,10 @@ buildPythonPackage rec {
     sha256 = "0pfqfr5xqgsqkxzrmj8xl2glyl4nbq0irs0k6ik7iy3gd3mxf5g1";
   };
 
+  postPatch = ''
+    substituteInPlace setup.py --replace '"pytest-runner"' ""
+  '';
+
   buildInputs = [ keyutils ];
   checkInputs = [ pytest pytest-runner ];