remove empty GtkTreeEntryClass

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74418 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
remove symbol exports, this code is private to the library

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74419 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775