Webpack config: Remove outdated comment

webpack.common.js

@@ -1,10 +1,6 @@
 const path = require('path');
 const webpack = require('webpack');
 
-// Target a version without class support due to this issue:
-// https://stackoverflow.com/q/43307607
-// This does not mean that we support Firefox <60ESR!
-// We will increase the target again once FF52 has died out.
 const babelOptions = {
   presets: [
     ['@babel/preset-env', {