Revert "Add a flag to d8 to invoke weak callbacks"

This reverts r21529.

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/302543004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21531 ce2b1a6d-e550-0410-aec6-3dcde31c8c00