Remove unused externals

Author: jakezatecky

webpack.config.js

@@ -38,14 +38,6 @@ function makeConfig({ target }) {
                     amd: 'react',
                 },
             },
-            {
-                'react-dom': {
-                    root: 'ReactDOM',
-                    commonjs2: 'react-dom',
-                    commonjs: 'react-dom',
-                    amd: 'react-dom',
-                },
-            },
         ],
         module: {
             rules: [