python3Packages.leather: fix build

Broken in 2f4ea0c6df.

Upstream changed from nose to pytest. Previously, the
setuptoolsCheckHook would run and execute the `./test.py` file, but that
is not part of upstream’s build process and doesn’t work. Including
pytestCheckHook means that does not run—just pytest.

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

@@ -4,7 +4,7 @@
 , six
 , cssselect
 , lxml
-, nose
+, pytestCheckHook
 }:
 
 buildPythonPackage rec {
@@ -22,15 +22,9 @@ buildPythonPackage rec {
   nativeCheckInputs = [
     cssselect
     lxml
-    nose
+    pytestCheckHook
   ];
 
-  checkPhase = ''
-    runHook preCheck
-    nosetests
-    runHook postCheck
-  '';
-
   meta = with lib; {
     homepage = "http://leather.rtfd.io";
     description = "Python charting library";