[bp/r52019][FIX] structures: No need to disable sortable on page list items as they're not sortable in the first place (presumably something in jquery-ui draggable has changed?)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@52020 b456876b-0849-0410-b77d-98878d47e9d5