Pop event handler from wxDVC edit control before destroying it.

Pop event handler from wxDVC edit control before destroying it.

This fixes the assert in wxWindow dtor checking that all event handlers pushed
on the window were removed.

Also fix a memory leak by not creating an unnecessary object of wxKillRef
class. In fact remove this class entirely.

Closes #11732.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64216 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775