Remove obsolete global V8::IsRunning() predicate.

R=yangguo@chromium.org
BUG=v8:2744

Review URL: https://codereview.chromium.org/23597013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16488 ce2b1a6d-e550-0410-aec6-3dcde31c8c00