g5k: Remove python3 interpreter override
This interpreter override was breaking support for CentOS nodes: #174 (closed)
The override was introduced because Ansible used to default to /usr/bin/python as interpreter, and we don't know if it's python2 or python3.
But since Ansible 5 (ansible-core 2.12.0), Ansible now defaults to python3: https://github.com/ansible/ansible/commit/fa7482c63a654e8bc602fa459aec7520d2fa6f23
As a result, this change should have no impact for people running Ansible 5 and above.
If you are using Enoslib with older versions of Ansible (2.9, 2.10, 3, 4), then the Python interpreter will now be back to the "/usr/bin/python" default.