bug#43065: Fix or remove broken flyspell-issue-welcome-flag option

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Wed, 26 Aug 2020 22:24:45 -0700
> 
> 1. Fix it.  I have attached a patch here which does that.  The message
>    is mildly annoying, but could be useful to beginners.  (And it's
>    easy to disabled using the mentioned variable.)
> 
> 2. Fix it, but change the default to nil.  I think this is pointless,
>    since this would mostly be useful to beginners.
> 
> 3. Remove the code and make the option obsolete.
> 
> Any opinions or preferences?

#1, please.

Thanks for paying attention to this.