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

[Stefan Kangas]

The flyspell-issue-welcome-flag option is supposed to control whether or
not a welcome message is shown when enabling flyspell-mode:

    "Welcome to Flyspell. Use C-. or Mouse-3 to correct words."

This does not work; flyspell-mode does not show such a message.

>From digging in the sources, it's not clear to me if this has worked at
all since 2002 or so.  I didn't bother with a full investigation, so I
might be overlooking something.

In any case, I see three options:

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?

txtYOEvgRVF80.txt
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0001-Fix-flyspell-welcome-message.patch
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