Remove unused methods about Node::class_id_

BUG=

Review URL: https://codereview.chromium.org/11983002
Patch from Kentaro Hara <haraken@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13407 ce2b1a6d-e550-0410-aec6-3dcde31c8c00