Drop nsfw support

[rschnekenbu]

NSFW (node-sentinel-file-watcher) is one of our dependencies and was not updated for the last 2 years.

In the context of #13957, there may be some evolution to do on the FileSystemWatcher mechanism, it could be a good point to evaluate changing this library to a newer one. In short about these evolutions:

• file-system-event-service-ext-impl.ts may follow evolutions as indicated in its comment
• the proposed API used by typescript require API and behavior evolution on our current framework.

As a note: VS Code is now using parcel (https://github.com/parcel-bundler/watcher).

[msujew]

For the necessary changes, see #12784 :)