bug#43323: Rename cua-mode to something better?

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Fri, 11 Sep 2020 12:19:51 -0700
> Cc: 43323@debbugs.gnu.org
> 
> Maybe we could just rename the section (info "(emacs) CUA Bindings")
> into something more descriptive?
> 
> The cua-mode doc string could also be improved to start with the part
> that says what it actually does.

Feel free to suggest the specific changes.