Remove highlightCode:true because it's now the default (facebook#5085)

Author: marcofugaro

config/webpack.config.dev.js

@@ -267,7 +267,6 @@ module.exports = {
                   cacheDirectory: true,
                   // Don't waste time on Gzipping the cache
                   cacheCompression: false,
-                  highlightCode: true,
                 },
               },
             ],
@@ -309,7 +308,6 @@ module.exports = {
                     'react-scripts',
                   ]),
                   // @remove-on-eject-end
-                  highlightCode: true,
                   // If an error happens in a package, it's possible to be
                   // because it was compiled. Thus, we don't want the browser
                   // debugger to show the original code. Instead, the code

config/webpack.config.prod.js

@@ -306,7 +306,6 @@ module.exports = {
                   // Save disk space when time isn't as important
                   cacheCompression: true,
                   compact: true,
-                  highlightCode: true,
                 },
               },
             ],
@@ -343,7 +342,6 @@ module.exports = {
                     'react-scripts',
                   ]),
                   // @remove-on-eject-end
-                  highlightCode: true,
                   // If an error happens in a package, it's possible to be
                   // because it was compiled. Thus, we don't want the browser
                   // debugger to show the original code. Instead, the code