Release bigdl-nano on PyPI don't allow direct urls in install_requires

[Le-Zheng]

jenkins: http://10.112.231.51:18888/view/ZOO-NB/job/Nano-NB-Deploy-PYTHON-PyPI/5/console HTTPError: 400 Client Error: Invalid value for requires_dist. Error: Can't have direct dependency: "torch-ipex @ https://intel-optimized-pytorch.s3.cn-north-1.amazonaws.com.cn/wheels/v1.8/torch_ipex-1.8.0-cp37-cp37m-linux_x86_64.whl ; extra == 'pytorch'" for url: https://upload.pypi.org/legacy/ Build step 'Execute shell' marked build as failure

It is a restriction that direct URLs like https://github.com/intel-analytics/analytics-zoo/blob/bigdl-2.0/python/nano/setup.py#L102 cannot occur in the requires-dist metadata element.

[yangw1234]

@leonardozcm would you mind looking at this issue? I think we can remove ipex and use the pytorch in pypi. If user use ipex plugin we raise an error telling user how to install ipex

[leonardozcm]

I see, I'm working on it.