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

[Eli Zaretskii <eliz@gnu.org>]

> From: Matt Armstrong <matt@rfc20.org>
> Date: Wed, 03 Mar 2021 18:29:28 -0800
> 
> I was scratching my head trying to figure out why overlays_at() had such
> a complex function signature.  It turns out that it does not need to be
> so complex now and, I think, it never did.
> 
> >From 0337e4823b32dd15bdae1f61df12b5f68170e360 Mon Sep 17 00:00:00 2001
> From: Matt Armstrong <matt@mdeb>
> Date: Wed, 3 Mar 2021 16:31:02 -0800
> Subject: [PATCH] Remove unecessary change_req arg from overlays_at()
> 
> The change_req arg was an unecessary complexity.  It only changed what
> might be assigned to the *prev_ptr arg, and all callers that passed a
> non-null prev_ptr also passed a true change_req.
> 
> This makes it clear that no caller desires the behavior that would
> have occurred with a non-null prev_ptr and a false change_req.
> 
> For archaeologists, the above invariants appear to have been true from
> the beginning, and whatever bug fixed by the commits below need not
> have been controlled with a new boolean arg.  See commits
> ac869cf715 ((overlays_at): Add CHANGE_REQ parameter, 2000-08-08) and
> 1d5f4c1de4 ((overlays_at): Only let CHANGE_REQ inhibit an assignment
> of startpos to prev when startpos == pos, 2000-10-25).

Could you please tell what are the benefits of this change?  The
signature may be complex, but it doesn't currently cause any problems,
does it?  I'd prefer not to change code that is working and causes no
trouble.

Thanks.