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`.
This reverts commit f20a36fcd8feed3671b4c1591dbf4a018eef4cd3, reversing
changes made to 15350df8d925a335e9004b6ce7219a6215df41d0.
I accidentally pressed the Merge button.
