[NFC][RISCV] Remove useless code in RISCVRegisterInfo.td.

Differential Revision: https://reviews.llvm.org/D94750

Author: Hsiangkai

llvm/lib/Target/RISCV/RISCVRegisterInfo.td

@@ -383,10 +383,6 @@ let RegAltNameIndices = [ABIRegAltName] in {
   def VXRM   : RISCVReg<0, "vxrm", ["vxrm"]>;
 }
 
-class RegisterTypes<list<ValueType> reg_types> {
-  list<ValueType> types = reg_types;
-}
-
 class VReg<list<ValueType> regTypes, dag regList, int Vlmul>
   : RegisterClass<"RISCV",
                   regTypes,