user32/tests: Remove SetShellWindowEx from test_shell_window.

[Gerald Pfeifer]

On Sun, 9 May 2010, testbot at testbot.winehq.org wrote:
> While running your changed tests on Windows, I think I found new 
> failures. Being a bot and all I'm not very good at pattern recognition, 
> so I might be wrong, but could you please double-check? Full results can 
> be found at http://testbot.winehq.org/JobDetails.pl?Key=1974

That really cannot be related to my test (unless there is some most
subtle timing issue involved, perhaps, which is completel unrelated).

It appears as if these tests all run into problems on the W7 flavor,
regardless and independently of my patch.

Gerald