Get wxPGProperty items to be deleted with deferral directly from the corresponding internal list of items.

Don't use iterator to collect wxPGProperty items in wxPropertyGridPageState::DoClear().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78069 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775