Remove postcss-bidirection and postcss-class-namespace from dev build (firefox-devtools#8155)

Author: Florens Verschelde

postcss.config.js

@@ -34,13 +34,11 @@ module.exports = ({ file, options, env }) => {
 
   return {
     plugins: [
-      require("postcss-bidirection"),
       require("autoprefixer")({
         browsers: ["last 2 Firefox versions", "last 2 Chrome versions"],
         flexbox: false,
         grid: false
       }),
-      require("postcss-class-namespace")(),
       mapUrl(mapUrlDevelopment)
     ]
   };