Revert "[CodeGen][X86] Expand USUBSAT to UMAX+SUB, also for vectors"

This reverts commit r351125.

I missed test changes in an SLPVectorizer test, due to the cost model
changes. Reverting for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351129 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed