Update packaging.md for Python 3 only packages (#21720)
Update packaging.md for Python 3 only packages (#21720)

* Update packaging.md

* 3.7 as minimal

* Stop checking if azure 0.x is installed

* TLDR version

* Not universal anymore

* Classifier Py3 Only

* Update packaging.md
Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python