bug#50999: 29.0.50; Deleting libraries obsolete since Emacs 24

[Stefan Kangas <stefan@marxist.se>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> > I would like to confirm that for Emacs 29.1 we want to delete libraries
> > obsoleted five major versions ago, i.e. those obsoleted in Emacs 24.
>
> That does seem logical, since we removed 23.3 stuff last time around.
> But shouldn't we delete 24.1 things only -- 24.1-24.5 are distinct
> releases (and not like 27.x and 28.x, which are only bugfix releases).
>
> I think.  I haven't actually looked on the timeline for the 24.x releases.

In Emacs 28.1, we deleted anything obsoleted in Emacs 23:

2012-01-29 - Emacs 23.4 released
2011-03-10 - Emacs 23.3 released
2010-05-08 - Emacs 23.2 released
2009-07-29 - Emacs 23.1 released

This is what the release schedule looked like for Emacs 24:

2016-09-17 - Emacs 25.1 released
2015-04-10 - Emacs 24.5 released
2014-10-20 - Emacs 24.4 released
2013-03-11 - Emacs 24.3 released
2012-08-27 - Emacs 24.2 released
2012-06-10 - Emacs 24.1 released

(Emacs 23 was around for ~3 years, but Emacs 24 was around for ~4.)

Assuming that Emacs 29 will be released in 2022 or 2023, removing
anything from 24.1-24.3 should mean it's been 9-10 years since the
libraries were obsoleted in an official release.  If we remove stuff
obsoleted in 24.4 and 24.5 as well, that would mean it's only been 7-8
years.  The former should be okay and in line with our historical
practice, the latter is a bit more enthusiastic and could be
discussed.

FWIW, it is kind of nice to have the easy to understand principle that
we generally delete obsolete stuff after five major releases, but it
is true that version 24 is somewhat different from 23, 25, 26 and 27
in that it was around for longer.

I think we should just decide what we want to do in Emacs 29, and then
apply the same principle for deleting obsolete functions, variables,
etc.