bug#64757: 30.0.50; Declare `defadvice` obsolete

[Eli Zaretskii]

> Date: Thu, 20 Jul 2023 18:05:40 -0400
> From:  Stefan Monnier via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Emacs-29 is the first release that doesn't use the old advice library in
> its own code at all, so I think Emacs-30 is a good time to mark
> `defadvice` as obsolete.
> 
> I suggest to do it with the following patch, which should not introduce
> any incompatibilities.

No objections from me.  However, ...

> diff --git a/etc/NEWS b/etc/NEWS
> index d1af3b1b866..54fb6ccac5c 100644
> --- a/etc/NEWS
> +++ b/etc/NEWS
> @@ -614,6 +614,8 @@ provokes an error if used numerically.
>  
>  * Lisp Changes in Emacs 30.1
>  
> +** 'defadvice' is marked as obsolete.

...this is too terse.  We need to mention the two alternatives to
defadvice, including pointers to the ELisp manual's nodes.  People who
still use defadvice will need those to convert their programs.