Revert "Return MaybeHandle from NewConsString."

This reverts r20473.

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/223593004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20475 ce2b1a6d-e550-0410-aec6-3dcde31c8c00