Remove redundant six dependency and upgrade syntax for Python 3

[hugovk]

This library no longer supports Python 2 but is still using and installing the six compat library as a dependency.

Let's remove it and use the standard library directly instead.

[tedder]

@hugovk can you rebase? I just committed code to fix the failing unit test.

Also curious if you have a reason for the wheel removal.

[hugovk]

@hugovk can you rebase? I just committed code to fix the failing unit test.

Done!

Also curious if you have a reason for the wheel removal.

Do you mean b8306c9 ?

It's not removing a wheel, but telling it not to create a "universal" wheel. Universal wheels are for when you want to support both Python 2 and Python 3, and are no longer needed for Python 3 only:

https://packaging.python.org/en/latest/guides/dropping-older-python-versions/#dealing-with-the-universal-wheels

[tedder]

It's not removing a wheel, but telling it not to create a "universal" wheel. Universal wheels are for when you want to support both Python 2 and Python 3, and are no longer needed for Python 3 only:

Perfect. I just didn't follow that.