Revert "Use %_IsSmi instead of %MaxSmi."

This reverts r17983.

TBR=danno@chromium.org

Review URL: https://codereview.chromium.org/79263005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17984 ce2b1a6d-e550-0410-aec6-3dcde31c8c00