Yt-dlp: External JavaScript runtime now required for full YouTube support

From

https://github.com/yt-dlp/yt-dlp/wiki/EJS

it looks like deno is recommended for these reasons:

> Notes

> * Code is run with restricted permissions (e.g, no file system or network access)

> * Supports downloading EJS script dependencies from npm (--remote-components ejs:npm).

It's fine for this project since google is probably not in the business of triggering exploits in yt-dlp users but please do not use deno sandboxing as a your main security measure to execute untrusted code. Runtime-level sandboxing is always very weak. Relying on OS-level sandboxing or VMs (firecracker & co) is the right way for this.