Remove unnecessary c_str() from wx var arg functions arguments

Using c_str() for arguments to wxString::Printf(), Format() and
wxLogXXX() is useless since wx 2.9 days, so simply remove them.

No real changes, this is just a (long due) cleanup.

src/common/fontcmn.cpp

@@ -713,7 +713,7 @@ void wxNativeFontInfo::SetFaceName(const wxArrayString& facenames)
 
     // set the first valid facename we can find on this system
     wxString validfacename = wxFontEnumerator::GetFacenames().Item(0);
-    wxLogTrace(wxT("font"), wxT("Falling back to '%s'"), validfacename.c_str());
+    wxLogTrace(wxT("font"), wxT("Falling back to '%s'"), validfacename);
     SetFaceName(validfacename);
 #else // !wxUSE_FONTENUM
     SetFaceName(facenames[0]);