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/pyasn1-modules/default.nix

@@ -1,7 +1,6 @@
 { stdenv, buildPythonPackage, fetchPypi, pyasn1, isPyPy }:
 
 buildPythonPackage rec {
-  name = "${pname}-${version}";
   pname = "pyasn1-modules";
   version = "0.2.1";
   disabled = isPyPy;