Don't double-check elements in the prototype chain in array builtins

BUG=
R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/701513002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25076 ce2b1a6d-e550-0410-aec6-3dcde31c8c00