Revert "Really skip dead blocks in GVN"

This reverts commit r19779 for breaking the GVN algorithm.

BUG=352149
LOG=y
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/200223004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19932 ce2b1a6d-e550-0410-aec6-3dcde31c8c00