delete py_bin for quant. Add message to indicate succesful finish (#61)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/61

instead of using buck for this we should do 'python3 -m examples.quantization.example --model_name mv2'

Reviewed By: larryliu0820

Differential Revision: D48325202

fbshipit-source-id: 09f8646ad2067c67e133852e7f4a633db263c737