Remove unnecessary c_str() calls from the samples

Pass wxStrings directly to wxString::Format("%s") and similar
pseudo-vararg functions, there is no need for c_str() there since
wxWidgets 2.9.

Closes https://github.com/wxWidgets/wxWidgets/pull/1009

samples/taborder/taborder.cpp

@@ -254,7 +254,7 @@ void MyFrame::OnIdle( wxIdleEvent& WXUNUSED(event) )
         wxString msg;
         if ( focus )
         {
-            msg.Printf("Focus is at %s", s_windowFocus->GetName().c_str());
+            msg.Printf("Focus is at %s", s_windowFocus->GetName());
         }
         else
         {