"remove rowwise_add no_gradient"

paddle/operators/rowwise_add_op.cc

@@ -51,8 +51,5 @@ for i in xrange(X.shape[0]):
 }  // namespace paddle
 
 REGISTER_OP(rowwise_add, ops::RowWiseAddOp, ops::RowWiseAddOpMaker);
-// REGISTER_GRADIENT_OP(rowwise_add, rowwise_add_grad, ops::RowWiseAddGradOp);
-NO_GRADIENT(rowwise_add);
-
 REGISTER_OP_CPU_KERNEL(rowwise_add,
                        ops::RowWiseAddKernel<ops::CPUPlace, float>);