chore: clean up unused browser-script deps + config (#61329)

tools/client-plugins/browser-scripts/webpack.config.cjs

@@ -93,17 +93,6 @@ module.exports = (env = {}) => {
         process: require.resolve('process/browser.js')
       },
       extensions: ['.js', '.ts']
-    },
-    // To keep the client React version decoupled from the curriculum React
-    // version we use externals to stops Webpack from bundling React and
-    // ReactDOM (they're fetched from the cdn when needed by the client or
-    // curriculum tests). react-dom/server and react-dom/test-utils are included
-    // separately because enzyme-adapter-react-16 imports them directly.
-    externals: {
-      react: 'React',
-      'react-dom': 'ReactDOM',
-      'react-dom/server': 'ReactDOMServer',
-      'react-dom/test-utils': 'ReactTestUtils'
     }
   };
 };