CI: Removing linting from windows

[cpcloud]

This is a workaround for the somewhat mysterious flake8 failures on Windows
so that we can get green builds.

[cpcloud]

@scottcode Merged this in the meantime to get passing builds. I'm not entirely sure what's happening here, but I don't have a windows box to debug this at the moment.

[scottcode]

@cpcloud I think it's reasonable to drop flake8 from Window, because it still gets done in the Linux environments. It's not really our job to test flake8's interoperability, just want to make sure the build conforms to the style.