bug#66636: Move lexical-binding warning from checkdoc to byte-compiler

[Eli Zaretskii]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Sat, 21 Oct 2023 11:53:58 +0200
> Cc: monnier@iro.umontreal.ca,
>  luangruo@yahoo.com,
>  66636@debbugs.gnu.org,
>  stefankangas@gmail.com
> 
> We certainly care about users of legacy code. The warning is intended as a 
> soft nudge to encourage users to convert their code to lexical binding, which 
> is quite straightforward most of the time.
> 
> When it's not, or when the user simply doesn't have the time or expertise to 
> perform the conversion, it's just a matter of inserting `-*- lexical-binding: 
> nil -*-`. Doing so will both silence the warning and buy the user some 
> reprieve. A lot of reprieve, in fact.
> 
> This should probably be pointed out in the NEWS entry as well.

If specifying lexical-binding:nil in the first line is the solution
for those who want to keep dynamically-bound code, then yes, it should
be definitely in NEWS, and probably also in the ELisp manual.