Removal of pyhon2 from the Azure IoT Edge Dev Tool

[konichi3]

We have removed python2 support from the Azure IoT Edge Dev Tool.

It speeds up your IoT Edge inner-loop dev (dev, debug, test) by reducing multi-step build & deploy processes into one-line CLI commands as well as drives your outer-loop CI/CD pipeline.

Release v3.0.0-rc · Azure/iotedgedev (github.com)

[#2]

We have released the iotedgedev tool v3.0.0.
https://github.com/Azure/iotedgedev/releases/tag/v3.0.0

The change from v.3.0.0 RC are as follows:
- Docker container supporting the updated pypi package
- The latest tag on both the container and the pypi package defaults to the versions that do not support python2

To get versions that support python2, you would need to check the pypi package v2.2.0 or the docker container v2.1.4.