wxPGProperty::Add(wxArrayString, ValArrItem), GetItemAtY() and HasValue() were documented but don't actually exist, remove them. Also correct wxPGProperty::Empty() scope: it's protected and not public. Closes #13988. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70607 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775