refactor(common): remove python3

Synchronizes with Zephyr documentation.

See: https://docs.zephyrproject.org/2.5.0/getting_started/index.html
See: https://docs.zephyrproject.org/2.5.0/getting_started/installation_linux.html#installation-linux
PR: #89

Author: innovaker

Dockerfile

@@ -18,7 +18,6 @@ RUN \
   gperf \
   make \
   ninja-build \
-  python3 \
   python3-dev \
   python3-pip \
   python3-setuptools \