Fix #4802: Ruffle conflicts with danbooru JS

Caused by Webpack clobbering the `Danbooru` variable for unknown reasons
when the app/javascript/packs/flash.js pack is loaded. Disabling the
output.library option seems to fix it.

config/webpack/base.js

@@ -1,9 +1,9 @@
 const { webpackConfig, merge } = require('@rails/webpacker')
 
 module.exports = merge(webpackConfig, {
-  output: {
+//  output: {
-    library: "Danbooru",
+//    library: "Danbooru",
-  },
+//  },
   resolve: {
     alias: {
       "jquery": "jquery/src/jquery.js",