bug#41026: Improve documentation of `makunbound' and `fmakunbound'

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Cc: 41026@debbugs.gnu.org
> Date: Sat, 02 May 2020 16:17:04 +0200
> 
> >> +The corresponding operation for functions is `fmakunbound'.  */)
> >    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > The "corresponding" part isn't accurate, is it?
> 
> Sorry, I thought it was.  But my understanding of this is probably
> much too naive.
> 
> Would we avoid the inaccuracy by deleting the word "corresponding"?

I'd just say "See also `fmakunbound'".  And the same in the
fmakunbound doc string.

Btw, why the link to the manual?  Does the manual say something
important that the doc strings don't?  If it does, perhaps we should
make the laconic doc string slightly more elaborate?