Created by: wangkuiyi

After a grep, I noticed two classes that overrides OperatorBase::Init:

1. RecurrentOp::Init():

   void RecurrentOp::Init() {
     OperatorBase::Init();
     std::unique_ptr<rnn::Argument> arg(new rnn::Argument());
     rnn::InitArgument(kArgName, arg.get(), *this);
     alg_.Init(std::move(arg));
   }

2. FullyConnectedOp::Init():

   void Init() override {
     AddOp(OpRegistry::CreateOp("mul",
                                {
                                    Input("X"), Input("W"),
                                },
                                {Output("before_act")},
                                {}));
     auto b = Input("b");
     if (b != EMPTY_VAR_NAME()) {
       AddOp(OpRegistry::CreateOp("rowwise_add",
                                  {Output("before_act"), Input("b")},
                                  {Output("before_act")},
                                  {}));
     }
   
     auto activation = GetAttr<std::string>("activation");
     AddOp(OpRegistry::CreateOp(
         activation, {Output("before_act")}, {Output("Y")}, {}));
     CompleteAddOp(false);
   }

It seems both code snippets can be moved into class constructors. Indeed, given that OperatorBase::Init() doesn't have any parameters, it doesn't provide any extra context than the constructor.