1. Remove unused dead functions.

2. Replace the virtual As-* type cast functions with non-virtual version
that uses node_type().

Result is around 13K reduction in binary size.
Review URL: http://codereview.chromium.org/8335006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9841 ce2b1a6d-e550-0410-aec6-3dcde31c8c00