testing: fix tests without cleanup in pytest.

It was broken by 89ffac3b01,
which added "cleanup" method to the base test class,
 resulting in reporting cleanup for all of the tests.

tests/atf_python/utils.py

@@ -50,7 +50,3 @@ def test_id(self):
     def setup_method(self, method):
         """Run all pre-requisits for the test execution"""
         self._check_modules()
-
-    def cleanup(self, test_id: str):
-        """Cleanup all test resources here"""
-        pass