bug#46915: [PATCH] Remove unecessary change_req arg from overlays_at()

[Eli Zaretskii <eliz@gnu.org>]

> From: Matt Armstrong <matt@rfc20.org>
> Cc: 46915@debbugs.gnu.org
> Date: Thu, 04 Mar 2021 12:03:59 -0800
> 
> So, the benefit of this change can be summarized:
> 
>  - We don't think the current overlay implementation is necessarily the
>    right thing, so we can presume that this area will change at some
>    point.
> 
>  - If we simplify the API, future changes will be easier to review.  In
>    particular, nobody will ever have to think about callers that want a
>    *PREV_PTR value with a false CHANGE_REQ, and no future implementer
>    will feel like they need to provide that functionality.

I'm okay with doing this nad similar changes as part of landing the
noverlay branch (or as part of some other similar redesign of how
overlays work in Emacs).  What I'd like to avoid is installing this
change separately, as if it alone has enough merit.  if the goal is to
replace the current implementation with a more efficient one, that's a
good change, and API simplifications could very well come with it.
But not without it and not ahead of it.

It's a bit like fixing whitespace: we don't like doing it in separate
changesets, but together with other significant changes in the same
area of the code.

So I urge you to continue the work on the noverlay branch, and if that
branch will come with this and other changes in the internal APIs,
that's fine by me.  My problem is only with installing API changes
right now, when we are not at all sure yet the overlays redesign will
indeed land any time soon.

OK?