bug#39546: 28.0.50; Do not require subr-x at run time

[Eli Zaretskii]

> From: Tino Calancha <tino.calancha@gmail.com>
> Cc: 39546@debbugs.gnu.org,  Eli Zaretskii <eliz@gnu.org>,
>   michael.albinus@gmx.de,  larsi@gnus.org
> Date: Mon, 10 Feb 2020 22:00:21 +0100
> 
> Tino Calancha <tino.calancha@gmail.com> writes:
> 
> >> I have run the testsuite without surprises.
> > Well, actually there was a surprise, but who don't like surprises after
> > all!
> Well, I must recognize I am one of those guys who doesn't like
> surprises.  It seems `when-let' became very popular these days.
> 
> Here is the updated patch.  It takes in account all usages of `when-let'
> once dropped the cookie.

Thanks.

Are we talking about doing these changes on master?  Because I think
such wide-sweeping changes that aren't bugfixes are not really
appropriate for the release branch.  If you want to move
replace-region-contents to replace.el on emacs-27, I agree, but all
the rest should go to master, I think.