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/webview/webview.cpp

@@ -769,7 +769,7 @@ void WebFrame::OnFindText(wxCommandEvent& evt)
     {
         count++;
     }
-    wxLogMessage("Searching for:%s  current match:%li/%i", m_findText.c_str(), count, m_findCount);
+    wxLogMessage("Searching for:%s  current match:%li/%i", m_findText, count, m_findCount);
 }
 
 /**