Remove some dead code

- I wrote a thing: https://github.com/asottile/dead
- wanted to try it out, there's lots of false positives and I didn't look
  through all the things it pointed out but here's some

testing/python/metafunc.py

@@ -784,7 +784,6 @@ class TestMetafuncFunctional(object):
 
             @pytest.fixture
             def metafunc(request):
-                assert request._pyfuncitem._genid == "0"
                 return request.param
 
             def test_function(metafunc, pytestconfig):