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`.
Also moved the expression from python-packages.nix to ./pkgs/development/python-modules/future/default.nix due to discussion in #26220
Used fetchPypi insted of fetchurl.