[RISCV][NFC] Remove redundant setOperationAction.

[HsiangKai]

Summary

ISD::INSERT_VECTOR_ELT is already set above.

[craig.topper]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

if (Subtarget.useRVVForFixedLengthVectors()) {
         // FIXME: Use SPLAT_VECTOR for all types? DAGCombine probably needs
         // improvements first.
         if (!Subtarget.is64Bit() && VT.getVectorElementType() == MVT::i64) {
           setOperationAction(ISD::SPLAT_VECTOR, VT, Legal);
           setOperationAction(ISD::SPLAT_VECTOR_PARTS, VT, Custom);
         }
 
         setOperationAction(ISD::VECTOR_SHUFFLE, VT, Custom);
-        setOperationAction(ISD::INSERT_VECTOR_ELT, VT, Custom);
 
         setOperationAction(
             {ISD::MLOAD, ISD::MSTORE, ISD::MGATHER, ISD::MSCATTER}, VT, Custom);
 
         setOperationAction({ISD::VP_LOAD, ISD::VP_STORE,
                             ISD::EXPERIMENTAL_VP_STRIDED_LOAD,
                             ISD::EXPERIMENTAL_VP_STRIDED_STORE, ISD::VP_GATHER,
                             ISD::VP_SCATTER},