python27Packages.pytestpep8: remove due to pytest v6 incompatibility

Remove ``pythonPackages.pytestpep8`` because:
* It has been abandoned upstream: no PyPi release since 2014
* It is no longer compatible with pytest v6+: I get an error pointing to
  https://docs.pytest.org/en/stable/deprecations.html#node-construction-changed-to-node-from-parent
  when I try to use it with ``pytestCheckHook`` (i.e. pytest v6.0+)
* It doesn't have a maintainer

pkgs/development/python-modules/pytest-pep8/default.nix

@@ -1,28 +0,0 @@
-{ stdenv, buildPythonPackage, fetchPypi
-, pytest, pytestcache, pep8 }:
-
-buildPythonPackage rec {
-  pname = "pytest-pep8";
-  version = "1.0.6";
-
-  src = fetchPypi {
-    inherit pname version;
-    sha256 = "06032agzhw1i9d9qlhfblnl3dw5hcyxhagn7b120zhrszbjzfbh3";
-  };
-
-  buildInputs = [ pytest ];
-  propagatedBuildInputs = [ pytestcache pep8 ];
-
-  checkPhase = ''
-    py.test
-  '';
-
-  # Fails
-  doCheck = false;
-
-  meta = with stdenv.lib; {
-    license = licenses.mit;
-    homepage = "https://pypi.python.org/pypi/pytest-pep8";
-    description = "pytest plugin to check PEP8 requirements";
-  };
-}

pkgs/top-level/python-packages.nix

@@ -5803,7 +5803,7 @@ in {
 
   pytest-pep257 = callPackage ../development/python-modules/pytest-pep257 { };
 
-  pytestpep8 = callPackage ../development/python-modules/pytest-pep8 { };
+  pytestpep8 = throw "pytestpep8 was removed because it is abandoned and no longer compatible with pytest v6.0"; # added 2020-12-10
 
   pytest-pylint = callPackage ../development/python-modules/pytest-pylint { };