[CodeGen] Remove shouldExpandPartialReductionIntrinsic() hook (NFC) (#161498)

This is unused. Targets can lower/expand the `PARTIAL_REDUCE_*` ISD
nodes.

Author: MacDue

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -480,13 +480,6 @@ class LLVM_ABI TargetLoweringBase {
     return true;
   }
 
-  /// Return true if the @llvm.vector.partial.reduce.* intrinsic
-  /// should be expanded using generic code in SelectionDAGBuilder.
-  virtual bool
-  shouldExpandPartialReductionIntrinsic(const IntrinsicInst *I) const {
-    return true;
-  }
-
   /// Return true if the @llvm.get.active.lane.mask intrinsic should be expanded
   /// using generic code in SelectionDAGBuilder.
   virtual bool shouldExpandGetActiveLaneMask(EVT VT, EVT OpVT) const {

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -8103,10 +8103,6 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     return;
   }
   case Intrinsic::vector_partial_reduce_add: {
-    if (!TLI.shouldExpandPartialReductionIntrinsic(cast<IntrinsicInst>(&I))) {
-      visitTargetIntrinsic(I, Intrinsic);
-      return;
-    }
     SDValue Acc = getValue(I.getOperand(0));
     SDValue Input = getValue(I.getOperand(1));
     setValue(&I,