Fix clearing wxPG

Properties deleted immediately in wxPropertyGridPageState::DoClear() should be first removed from the lists of pending deletions.

Closes #16617

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78014 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775