bug#56641: Deprecate `lsh`

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Tue, 19 Jul 2022 15:38:29 +0200
> 
> The function `lsh` works almost like `ash` but is much slower, cannot be 
> constant-folded by the compiler, and above all has confusing semantics for 
> historical reasons. Using `lsh` instead of `ash` is always a mistake.
> 
> For these reasons we should deprecate `lsh`. It is not important to remove it 
> as soon as possible, but to dissuade people from accidentally using it in 
> their code.

The ELisp manual already says that ash is a better alternative, but
lsh has its niche, and I see no reason to deprecate it more than the
manual already does.

So, no, please let's not.