Move the cleaning of the `wp-includes/css/dist` folder from `clean:css` to `clean:webpack-assets` to avoid an order of operations issue in which the files were built shortly before been deleted later in the build process.
Follow up to [51689].
Props netweb, ramonopoly, peterwilsoncc.
Fixes#53719.
Built from https://develop.svn.wordpress.org/trunk@51713
git-svn-id: http://core.svn.wordpress.org/trunk@51319 1a063a9b-81f0-0310-95a4-ce76da25c4cd