don't use gtk_notebook_insert_page() return value as some old GTK+ versions (the...

don't use gtk_notebook_insert_page() return value as some old GTK+ versions (the one in Solaris 9 for instance) don't have it; also don't use gtk_notebook_get_nth_page() which we need this return value for at all in the trunk as it seems to be unnecessary

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52841 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775