python3Packages.cairocffi: fix cross-compilation, patch out unneeded tests

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

···
 , makeFontsConf
 , freefont_ttf
 , pytest
-, pytest-runner
 , glibcLocales
 , cairo
 , cffi

pkgs/development/python-modules/cairocffi/generic.nix

···
     fontDirectories = [ freefont_ttf ];
   };
 
-  checkInputs = [ numpy pytest pytest-runner glibcLocales ];
   propagatedBuildInputs = [ cairo cffi ] ++ lib.optional withXcffib xcffib;
+  propagatedNativeBuildInputs = [ cffi ];
+
+  # pytestCheckHook does not work
+  checkInputs = [ numpy pytest glibcLocales ];
+
+  postPatch = ''
+    substituteInPlace setup.cfg \
+      --replace "pytest-runner" "" \
+      --replace "pytest-cov" "" \
+      --replace "pytest-flake8" "" \
+      --replace "pytest-isort" "" \
+      --replace "--flake8 --isort" ""
+  '';
 
   checkPhase = ''
     py.test $out/${python.sitePackages}