Remove the dims checking when the dim is 3 (test=develop)

paddle/fluid/operators/activation_mkldnn_op.cc

@@ -100,9 +100,6 @@ void eltwise_forward(const framework::ExecutionContext &ctx,
   const T *x_data = x->data<T>();
   T *y_data = y->mutable_data<T>(ctx.GetPlace());
 
-  PADDLE_ENFORCE(x->dims().size() == 2 || x->dims().size() == 4,
-                 "Input dim must be with 2 or 4");
-
   std::vector<int> src_tz = framework::vectorize2int(x->dims());
 
   auto src_format =