Remove assertion scopes from V8_Fatal

V8_Fatal no longer tries to print a js stack, so we don't need those
scopes

BUG=none
R=yangguo@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/239293002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20777 ce2b1a6d-e550-0410-aec6-3dcde31c8c00