python2Packages: remove superfluous overrides

Since Python 2 is not supported anymore we only keep those overrides
which are used by leaf packages.

pkgs/development/python-modules/nbformat/2.nix

@@ -1,41 +0,0 @@
-{ lib
-, buildPythonPackage
-, fetchPypi
-, pytest
-, glibcLocales
-, ipython_genutils
-, traitlets
-, testpath
-, jsonschema
-, jupyter_core
-}:
-
-buildPythonPackage rec {
-  pname = "nbformat";
-  version = "4.4.0";
-
-  src = fetchPypi {
-    inherit pname version;
-    sha256 = "f7494ef0df60766b7cabe0a3651556345a963b74dbc16bc7c18479041170d402";
-  };
-
-  LC_ALL="en_US.utf8";
-
-  checkInputs = [ pytest glibcLocales ];
-  propagatedBuildInputs = [ ipython_genutils traitlets testpath jsonschema jupyter_core ];
-
-  preCheck = ''
-    mkdir tmp
-    export HOME=tmp
-  '';
-
-  # Some of the tests use localhost networking.
-  __darwinAllowLocalNetworking = true;
-
-  meta = {
-    description = "The Jupyter Notebook format";
-    homepage = "https://jupyter.org/";
-    license = lib.licenses.bsd3;
-    maintainers = with lib.maintainers; [ globin ];
-  };
-}