bug#44018: Don't consider play-sound-file to be a 'safe' function

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Thu, 15 Oct 2020 18:55:26 +0200
> 
> We should remove play-sound-file from the list of 'safe' functions in 
> unsafep.el.
> The risks outweigh the benefits here; this is just basic security engineering.
> The attack surface of play-sound-file is considerable.

Any details for the uninitiated, or pointers to the info?

Are the risks the same on all the supported platforms, or just on
some?

Thanks.