[RISCV] Remove untested code from SelectAddrRegRegScale.

This code handled load/store address that are a SHL instruction.
That seems very unlikely to occur unless you're accessing an array
that starts at address 0. I'm not even sure if you can represent
that in llvm IR.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

@@ -2824,10 +2824,6 @@ bool RISCVDAGToDAGISel::SelectAddrRegRegScale(SDValue Addr,
       Base = Addr.getOperand(0);
       return true;
     }
-  } else if (UnwrapShl(Addr, Index, Scale)) {
-    EVT VT = Addr.getValueType();
-    Base = CurDAG->getRegister(RISCV::X0, VT);
-    return true;
   }
 
   return false;