[RISCV][NFC] Remove unused variable

Remove unused variable in RISCVTargetLowering

Author: mshockwave

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -9618,7 +9618,6 @@ SDValue RISCVTargetLowering::lowerINSERT_VECTOR_ELT(SDValue Op,
 
   // If we know the index we're going to insert at, we can shrink Vec so that
   // we're performing the scalar inserts and slideup on a smaller LMUL.
-  MVT OrigContainerVT = ContainerVT;
   SDValue OrigVec = Vec;
   std::optional<unsigned> AlignedIdx;
   if (auto *IdxC = dyn_cast<ConstantSDNode>(Idx)) {