python-packages: clean up meta attribute

- Typos: meta.maintainer -> meta.maintainers, licences -> license, ...
- Remove unnecessary stdenv.lib (already in scope for entire file)
- [ maintainers.foo maintainers.bar ] -> with maintainers; [ foo bar ]
  Doing so even for single-maintainer packages makes it slightly
  more inviting to add others, which can only be a good thing.