This also throws out the SCEV reference counting scheme, as the the SCEVs now have a lifetime controlled by the
ScalarEvolution pass.
Note that SCEVHandle is now a no-op, and will be remove in a future commit.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73892 91177308-0d34-0410-b5e6-96231b3b80d8