Copy translations to wp.org and remove files from plugin

[JoryHogeveen]

These files aren't needed anymore. We should copy it to translate.wordpress.org and remove the files once the translations are accepted.

Existing languages Available on wp.org and removed in plugin are marked as complete https://translate.wordpress.org/projects/wp-plugins/widget-css-classes

• [x] nl_NL
• [x] ru_RU
• [ ] es_ES
• [ ] pl_PL
• [ ] sk_SK
• [ ] sr_RS
• [x] sv_SE

[JoryHogeveen]

sv_SE can be removed: https://translate.wordpress.org/locale/sv/default/wp-plugins/widget-css-classes