bug#22692: docstring for xref-find-definitions

[Eli Zaretskii]

> Cc: 22692@debbugs.gnu.org, juri@linkov.net, m.kupfer@acm.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sat, 27 Feb 2016 14:35:20 +0200
> 
> On 02/27/2016 12:32 PM, Eli Zaretskii wrote:
> 
> > The current doc string looks OK to me: it describes the behavior very
> > well.
> 
> Great. I believe the only thing holding this bug is making the choice 
> about the "valid" in the manual.

You mean, whether to remove the "valid" part from the 2nd sentence
reproduced below?

     ‘M-.’ (‘xref-find-definitions’) shows the definitions of the
  identifier at point.  With a prefix argument, or if there’s no valid
  identifier at point, it prompts for the identifier.            ^^^^^

I'd say let's remove it.