Don't set even try to set focus to wxPopupWindow itself in wxMSW.

Don't set even try to set focus to wxPopupWindow itself in wxMSW.

This doesn't work anyhow with our popup window implementation (it's a child of
the desktop and we can't set focus to it) and provokes error messages due to
::SetFocus() failures, so simply don't do this at all.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74676 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775