Revert "Expose the content of Maps and WeakMaps through MapMirror."

This reverts r22452.

TBR=amikhaylova@google.com

Review URL: https://codereview.chromium.org/399963002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22454 ce2b1a6d-e550-0410-aec6-3dcde31c8c00