Revert "More aggressive reuse of spill slots in the register allocator."

This reverts commit r23532 for introducing bunch of flakes.

TBR=titzer@chromium.org

Review URL: https://codereview.chromium.org/519423002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23533 ce2b1a6d-e550-0410-aec6-3dcde31c8c00