Don't use "Cancel" button in the about dialog of the listctrl sample.

No real changes, just remove the unnecessary button.

See #14618.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73238 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/listctrl/listtest.cpp

@@ -337,7 +337,7 @@ void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
 void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
 {
     wxMessageDialog dialog(this, wxT("List test sample\nJulian Smart (c) 1997"),
-            wxT("About list test"), wxOK|wxCANCEL);
+            wxT("About list test"));
 
     dialog.ShowModal();
 }