treewide: remove dead pytestpep8 references

pytestpep8 was removed in 25c9946f95.
This removes pytestpep8 in the rest of the tree, where it was hardly
used.

pkgs/development/python-modules/progressbar2/default.nix

@@ -6,7 +6,6 @@
 , python-utils
 , sphinx
 , flake8
-, pytestpep8
 , pytest-flakes
 , pytestcov
 , pytestcache
@@ -26,7 +25,7 @@ buildPythonPackage rec {
   propagatedBuildInputs = [ python-utils ];
   nativeBuildInputs = [ pytestrunner ];
   checkInputs = [
-    pytest sphinx flake8 pytestpep8 pytest-flakes pytestcov
+    pytest sphinx flake8 pytest-flakes pytestcov
     pytestcache freezegun
   ];
   # ignore tests on the nix wrapped setup.py