Revert "[BDCE][DemandedBits] Detect dead uses of undead instructions"

This reverts commit r349674. It causes a failure in
test-suite enc-3des.execution_time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349684 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed