Atom test fix

[Dmitry Timoshkov]

"Francois Gouget" <fgouget at free.fr> wrote:

> Conformance tests must not use Wine-specific headers (like
> wine/unicode.h) otherwise they will not compile on Windows.
> 
> wine/test.h is the only exception.
> 
> Changelog:
> 
>  * dlls/kernel/tests/atom.c
> 
>    Do not include wine/unicode.h
>    Duplicate strlenW

I would suggest to simply replace it by lstrlenW, instead of duplicating
code.

-- 
Dmitry.