shell32/tests: Fix a test on Win2k platform and above.

[Nicolas Le Cam]

Try2: Follow Vincent Povirk's suggestion of removing calls to
SetWindowLongPtr before destroying windows

Could someone test this patch on Win9x or WinNT ?

On Win2k (and according to test.winehq.org on above platforms) an
ABN_POSCHANGED message is sent to the last window that is removed.

This patch change the ok to a win_skip in this case.

Tell me if you have a better solution.

Nicolas Le Cam