Revert "[DAGCombiner] Add vector demanded elements support to computeKnownBits"

This seems to have increased LTO compile time bejond 2x of previous builds.
See http://lab.llvm.org:8080/green/job/clang-stage2-configure-Rlto/10676/

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285381 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed