It won't be enough to fix cross in all cases, but it is in at least
one: pywayland. I've only made the change in cases I'm confident it's
correct, as it would be wrong to change this when python.interpreter
is used in wrappers, and possibly when it's used for running tests.
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`.
