multimedia/mpv: Disable YTDLP option by default
The www/yt-dlp dependency now requires npm and deno as dependencies (via www/py-yt-dlp-ejs). This pulls in a bunch of build and run
dependencies which were not previously required.
There are two main downsides to this:
- Exploding build times
- Installing multimedia/mpv on a system now also installs a javascript interpreter which violates POLA and is generally not desirable.
Therefore, we're disabling the YTDLP option by default.
PR: 293736
Approved by: makc (multimedia)