Remove stylelint middleware

[eliperelman]

Closes #805.
Closes #982.

We cannot seem to get a recent release of stylelint-webpack-plugin [1] in order to provide any value.

[1] webpack-contrib/stylelint-webpack-plugin#149

[edmorley]

To add some additional reasons from IRC:

1. unlike the eslint related presets in this repository, the @neutrinojs/stylelint preset doesn't actually have much to configure, and doesn't really change it's behaviour based on other presets (compared to say the interactions between the JS linting presets when using the react/preact/vue/node presets). As such it doesn't save much work over people just adding stylelint-webpack-plugin directly in their .neutrinorc.js.
2. for CSS I don't think there's as much value for "linting during the build", compared to JS. For example, one advantage of eslint-loader is that it can give a useful linting error that might prevent/explain a runtime exception that would otherwise mean opening the browser console and figuring out why the app broke. That kind of scenario is much less likely to occur with CSS. As such a yarn lint:style that runs the styelint CLI outside of the webpack build, or an editor/IDE plugin would likely be sufficient for many cases.
3. Given (2), one option would be for us to ditch the stylelint-webpack-plugin part of @neutrinojs/stylelint and just keep the neutrino().stylelintrc() config generation for use with the stylelint CLI. However given (1), it doesn't seem like that adds any value over people just using a static config in .stylelintrc.js and not using Neutrino for it at all.

[timkelty]

@edmorley @eliperelman late response again guys, but I totally agree. Trim the fat!