Remove worker-loader (#23548)
[`worker-loader`](https://github.com/webpack-contrib/worker-loader) is
deprecated since webpack 5 which can load workers without it now, so
remove it. I think it was already dysfunctional because the regex does
not match our current worker scripts:
```
web_src/js/features/eventsource.sharedworker.js
web_src/js/features/serviceworker.js
web_src/js/serviceworker.js
```
I did confirm that eventsource worker still loads via simple
`console.log` inside the script.
Co-authored-by: delvh <leon@kske.dev>
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