bug#19423: 25.0.50; incompatible change to `make-obsolete' - added 3rd arg should be optional

[Drew Adams]

> > It misleads.  There is no need for such a "warning" - nothing to
> > warn users about, since the argument is optional.  It serves
> > no useful purpose.
> 
> While the argument is still optional now, it won't be, at some point
> in the future. 

Why should it?

> And there's a good reason to require this argument: people
> should annotate each obsoletion with the version when it happened.

That is *not* a good reason to make the argument mandatory.

That is a good reason to document why they should do so and
thus encourage them to do so.  Making such an argument
mandatory for that reason alone is quite misguided.

> That change was made 5 years ago; let it go.

It is trivial to fix the mistake, no matter how long ago
it was made.  Again, there is no good reason *not* to fix
this.