Revert r373172 "[X86] Add custom isel logic to match VPTERNLOG from 2 logic ops."

This seems to be causing some performance regresions that I'm
trying to investigate.

One thing that stands out is that this transform can increase
the live range of the operands of the earlier logic op. This
can be bad for register allocation. If there are two logic
op inputs we should really combine the one that is closest, but
SelectionDAG doesn't have a good way to do that. Maybe we need
to do this as a basic block transform in Machine IR.

llvm-svn: 373401