Remove special frontend for callbacks with slow-mode holders.
BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/436273002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22856 ce2b1a6d-e550-0410-aec6-3dcde31c8c00