bug#54046: emacs: Remove GNOME MediaKeys support

[Po Lu]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> The only mention I can find of "MediaKeys" in the Emacs sources are in
> examples in manuals and doc strings:
>
> @result{} (("/org/gnome/SettingsDaemon/MediaKeys"
>      ("org.gnome.SettingsDaemon.MediaKeys")
>
> Jeremy, is this what you had in mind?

If that's indeed what Jeremy had in mind, then IMO we should postpone
updating the documentation to remove those mentions until GNOME 42 is
released, otherwise it will not represent what is canonically installed
on a up-to-date system.

Thanks.