Created by: baiyfbupt

1. Fix some PaddleSlim distillation demo configs.

• Modify resnet34_resnet50_distillation.yaml to fit https://github.com/PaddlePaddle/models/pull/3483 resnet34 change.
• Modify mobilenetv1_resnet50_distillation.yaml try to avoid fsp_loss=NAN issue while training.

2. Remove some redundant code.