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/Theano/default.nix

@@ -40,7 +40,6 @@ let
   libgpuarray_ = libgpuarray.override { inherit cudaSupport; };
 
 in buildPythonPackage rec {
-  name = "${pname}-${version}";
   pname = "Theano";
   version = "1.0.2";