Undeprecate Persistent::ClearAndLeak

We depend on this in blink, and won't be able to replace it in
the near future

R=svenpanne@google.com, svenpanne@chromium.org
BUG=none
LOG=n

Review URL: https://codereview.chromium.org/95003004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18128 ce2b1a6d-e550-0410-aec6-3dcde31c8c00