Remove unneeded url lib (facebook#1715)

Remove unused `url` import in Webpack config

Author: pd4d10

config/webpack.config.prod.js

@@ -15,7 +15,6 @@ var HtmlWebpackPlugin = require('html-webpack-plugin');
 var ExtractTextPlugin = require('extract-text-webpack-plugin');
 var ManifestPlugin = require('webpack-manifest-plugin');
 var InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
-var url = require('url');
 var paths = require('./paths');
 var getClientEnvironment = require('./env');