Remove pycodestyle configuration from setup.cfg

[seanh]

Since it's now possible to move the setuptools configuration from setup.cfg into pyproject.toml (#53) if we can also get the pycodestyle configuration out of setup.cfg then we could get rid of the setup.cfg file entirely and have one less root file.

pycodestyle doesn't support pyproject.toml and it doesn't look like they're going to be adding support any time soon, so for the time being we have two options:

1. pycodestyle does support reading its configuration from tox.ini so we could move the pycodestyle config from setup.cfg into tox.ini. See https://pycodestyle.pycqa.org/en/latest/intro.html#configuration
2. We could remove pycodestyle from our projects. How much value does it really provide given that we have Black, isort and Pylint? There's a list of pycodestyle's warnings here: https://pycodestyle.pycqa.org/en/latest/intro.html#error-codes At a glance it doesn't look like to me like pycodestyle is providing any value. All of the warnings look like things that should never happen to Black- and isort-formatted code apart from a handful of warnings that I think Pylint might already cover anyway