Revert "[Unroll] Implement a conservative and monotonically increasing cost...

Revert "[Unroll] Implement a conservative and monotonically increasing cost tracking system during the full unroll heuristic analysis that avoids counting any instruction cost until that instruction becomes "live" through a side-effect or use outside the..."

This reverts commit r269388.

It caused some bots to fail, I'm reverting it until I investigate the
issue.

llvm-svn: 269395