ethereumjs/util require node polyfill for browser

[wighawag]

I have an issue with @ethereumjs/util It needs a node polyfill for the browser, which ideally shouldn't be necessary in a browser environment.

Here is the link to the imports in question

https://github.com/ethereumjs/ethereumjs-monorepo/blob/ee8e02f7be14f4311c2a967d9b8d9dd3ffc72166/packages/util/src/asyncEventEmitter.ts#L10