Revert "Bootstrapper::DetachGlobal also need to unset global_proxy's constructor to remove all refs to context"

This reverts r22460 for potentially breaking the mac webkit build.

TBR=titzer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/401813002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22474 ce2b1a6d-e550-0410-aec6-3dcde31c8c00