bug#31852: Make memory-limit obsolete

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 31852@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 16 Jun 2018 06:38:55 -0700
> 
> Eli Zaretskii wrote:
> > I don't understand what we gain by declaring
> > this tiny function obsolete
> 
> Nobody uses the function (clearly, since it doesn't work) so we gain simplicity, 
> which is a win.

If nobody uses the function, I see no gain at all, because obsoleting
a function tells those who use it not to.

> > Wouldn't it be enough just to add to the function's
> > documentation a note that the estimation should be expected to be
> > inaccurate with modern memory-management technologies?
> 
> Complicating the documentation would work against the goal of
> simplicity.

Then let's just move this to Lisp, and do nothing else.  That's even
simpler, IMO.