Revert "Load the global proxy from the context of the target function."

This reverts commit https://code.google.com/p/v8/source/detail?r=18458, since it exhibits a bug that breaks some tests.

TBR=verwaest@chromium.org
BUG=

Review URL: https://codereview.chromium.org/93863006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18461 ce2b1a6d-e550-0410-aec6-3dcde31c8c00