[RISCV] Remove unused function declaration. NFC

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -959,7 +959,6 @@ class RISCVTargetLowering : public TargetLowering {
   SDValue lowerFixedLengthVectorSelectToRVV(SDValue Op,
                                             SelectionDAG &DAG) const;
   SDValue lowerToScalableOp(SDValue Op, SelectionDAG &DAG) const;
-  SDValue lowerUnsignedAvgFloor(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerIS_FPCLASS(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerVPOp(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerLogicVPOp(SDValue Op, SelectionDAG &DAG) const;