Code review comment for ~cjwatson/lazr.restful:remove-six

All but one of the `six.ensure_*` calls that I removed are themselves in test code, so it's fairly easy to see that they're covered. The one exception is in `lazr.restful.declarations._versioned_class_name`, which is called by `lazr.restful.declarations.generate_*`. For removing `six.ensure_str` to be a problem there, somebody would have to have explicitly included a bytes item in their `IWebServiceConfiguration.active_versions`, which is declared as a list of `TextLine`; so I don't think this can be a problem.

Coverage seems to work fine for me, but declaring `coverage:run` would help so that it doesn't try to consider coverage of all dependencies as well. I'll propose a separate branch to set up coverage.