Revert "ES6: Add support for Map/Set forEach"

This reverts https://code.google.com/p/v8/source/detail?r=20823

It broke Windows builds. Will need to find a Windows try bot to figure
out why.

TBR=mstarzinger@chromium.org,arv@chromium.org

Review URL: https://codereview.chromium.org/238973011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20824 ce2b1a6d-e550-0410-aec6-3dcde31c8c00