object-literals with few elements but large element indices.

We can decide at parse time whether the created object literal should
have fast-case of slow-case elements.

Remove unused runtime function.
Review URL: http://codereview.chromium.org/805004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4100 ce2b1a6d-e550-0410-aec6-3dcde31c8c00