pythonPackages: remove name attribute`

The `buildPython*` function computes name from `pname` and `version`.
This change removes `name` attribute from all expressions in
`pkgs/development/python-modules`.

While at it, some other minor changes were made as well, such as
replacing `fetchurl` calls with `fetchPypi`.

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

@@ -3,7 +3,6 @@
 buildPythonPackage rec {
   pname = "aenum";
   version = "2.1.2";
-  name = "${pname}-${version}";
 
   src = fetchPypi {
     inherit pname version;