Clean up after r16292 (disable optimization for StringWrappers).

R=jochen@chromium.org
BUG=v8:2855

Review URL: https://codereview.chromium.org/22891028

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16677 ce2b1a6d-e550-0410-aec6-3dcde31c8c00