bug#28597: 26.0.60; [Security] Configure should use --without-pop by default

[Eli Zaretskii]

> Cc: jwiegley@gmail.com, 28597@debbugs.gnu.org, rpluim@gmail.com
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 2 Oct 2017 11:00:47 -0700
> 
> Users accustomed to other email clients are likely to expect that Emacs 
> "pop:whatever" will do something similar.

I'm dubious.  And I don't see how setting up other MUA is of any use
here, because we also use an encrypted POP3 connection
_if_it's_available_, e.g. via Mailutils, Gnus, etc.

But nagging users each time they invoke movemail to fetch via POP3 is
IMO unacceptable.  I'm sick and tired of similar nagging from Firefox,
and I definitely will object that Emacs behaves the same.  We
shouldn't patronize our users to that degree.  Let the Emacs packagers
worry about making their distributions more secure e,g, by depending
on Mailutils.

Anyway, I think we've cut enough slices of this salami, so let's stop,
and let's leave those who want to use POP3 nonetheless to their
devices.