text: Title: Please provide updated example code of pruning
  Body: <!-- Please only use this template for submitting enhancement requests -->
  
  
  **What would you like to be added**:
  provide updated example code of pruning
  
  **Why is this needed**:
  I got warning: `WARNING: The old API trainer,traced_optimizer,criterion,training_batches,mode,dummy_input will be deprecated after NNI v3.0, please using the new one evaluator,training_steps,mode,dummy_input` when runing the example pruning code from [here](https://github.com/microsoft/nni/blob/master/examples/model_compress/pruning/activation_pruning_torch.py). As far as i know, other pruning api have the same warning like TaylorFOWeightPruner, ADMMPruner etc.
  
  **Without this feature, how does current nni work**：
  It can work in nni 2.9, but after nni 3.0, the api will deprecated
  
  **Components that may involve changes**:
  
  **Brief description of your proposal if any**:
  