python3Packages.pyfakefs: remove unused 'undefined' dependency

This was a dependency used only in check phase.
It was removed upstream [1] to reduce closure size.
This change is helpful for nix, as `pyfakefs` is used in our distutils too.

The first release containing this change was 5.4.0.
There previously was a discussion [2] about this change upstream.

[1] https://github.com/pytest-dev/pyfakefs/commit/c3a1cc8d43ec17630404deb33c641b2012e652ac
[2] https://github.com/pytest-dev/pyfakefs/discussions/981

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

···
   # tests
   pandas,
   pytestCheckHook,
-  undefined,
 }:
 
 buildPythonPackage rec {
···
   nativeCheckInputs = [
     pandas
     pytestCheckHook
-    undefined
   ];
 
   pytestFlagsArray = [