Enable test for wxEVT_SHOW for non-MSW platforms too

This test does pass with wxGTK, so run it there.

tests/controls/windowtest.cpp

@@ -54,8 +54,6 @@ protected:
     wxDECLARE_NO_COPY_CLASS(WindowTestCase);
 };
 
-#if defined(__WXMSW__)
-
 static void DoTestShowHideEvent(wxWindow* window)
 {
     EventCounter show(window, wxEVT_SHOW);
@@ -89,8 +87,6 @@ TEST_CASE_METHOD(WindowTestCase, "Window::ShowHideEvent", "[window]")
     }
 }
 
-#endif // __WXMSW__
-
 TEST_CASE_METHOD(WindowTestCase, "Window::KeyEvent", "[window]")
 {
 #if wxUSE_UIACTIONSIMULATOR