bug#34663: remove ftx font backend

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: 34663@debbugs.gnu.org,  stefan@marxist.se
> Date: Tue, 07 Jan 2020 08:14:48 +0100
> 
>     >> Can we do something similar for XFT (and flip --with-cairo to
>     >> enabled)?
> 
>     Eli> I understand about enabling Cairo, but what exactly are you proposing
>     Eli> to do with XFT?
> 
> Add an entry to NEWS on master that itʼs deprecated and will be
> removed, and add verbiage to configure telling people to install cairo
> development packages if XFT is detected. That means weʼd remove XFT in
> emacs-29.

But removing XFT basically means we are deprecating non-Cairo builds
on X.  Is that really what we want to do?