[VPlan] Remove dead code for scalar VFs in VPRegionBlock::cost (NFC).

The VPlan cost model is not used to compute costs of scalar VFs
currently, as conversion to replicate regions makes accurately computing
the original scalar cost difficult.

Remove left over, dead code.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -845,19 +845,10 @@ InstructionCost VPRegionBlock::cost(ElementCount VF, VPCostContext &Ctx) {
   if (VF.isScalable())
     return InstructionCost::getInvalid();
 
-  // First compute the cost of the conditionally executed recipes, followed by
-  // account for the branching cost, except if the mask is a header mask or
-  // uniform condition.
-  using namespace llvm::VPlanPatternMatch;
+  // Compute and return the cost of the conditionally executed recipes.
+  assert(VF.isVector() && "Can only compute vector cost at the moment.");
   VPBasicBlock *Then = cast<VPBasicBlock>(getEntry()->getSuccessors()[0]);
-  InstructionCost ThenCost = Then->cost(VF, Ctx);
-
-  // For the scalar case, we may not always execute the original predicated
-  // block, Thus, scale the block's cost by the probability of executing it.
-  if (VF.isScalar())
-    return ThenCost / getPredBlockCostDivisor(Ctx.CostKind);
-
-  return ThenCost;
+  return Then->cost(VF, Ctx);
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)