Reenable tests that need to access the default timezone.

It's now available via builtins.

BUG=v8:2475
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/21512002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16016 ce2b1a6d-e550-0410-aec6-3dcde31c8c00