class_docstr: A model with the top layer removed, and with a new method `get_output_size` to retrieve the
  output channel size of the model.
  
  :param model_without_top: (nn.Module) A Model with the top layer removed.
  :param output_size: (int) Output channel size of the model.
code: def __init__(self, model_without_top: nn.Module, output_size: int):
      super(BackboneModule, self).__init__()
      self.net = model_without_top
      self.output_size = output_size
  
file_path: BigDL/python/nano/src/bigdl/nano/pytorch/vision/models/_utils.py
imports: from torch import nn
label_desc: Use image node_id 1 to create a new BackboneModule object from inherited base classes: nn with example: obj = BackboneModule(model_without_top, output_size)