Rather than using autodiscovery, the checkPhase should import
`__init__.py` from `diff_match_patch.tests to execute all relevant
tests. Otherwise several python2-related tests are executed in a py3 env
and break the build.
See also: https://hydra.nixos.org/build/102482273
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`.
