bug#37178: 26.2; doc strings of `eshell' and `eshell-buffer-name'

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Sat, 19 Oct 2019 14:22:20 +0200
> Cc: 37178@debbugs.gnu.org
> 
> It picks <4> in this case, which I think makes sense.  But I don't
> think the doc string needs to go into that level of detail, since that
> part of the behaviour is less important than the use cases:

I think we don't need to document this specifically, because the
special interpretation of just "C-u" is well documented in the Emacs
manual, and should be familiar to users.