Remove remnant from deferred error formatting on GC.

Deferred error formatting on GC was a failed experiment. It has been
removed, except for this part.  See r13371.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/233163004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20672 ce2b1a6d-e550-0410-aec6-3dcde31c8c00