Injected role vars, in cases where the vars were not generated
within the playbook run, are not ideal. In the case of our venv vars,
it removes the ability for a deploy to manipulate the venv download
tag or path using group vars.
This cleanup standardizes the venv tag and download url vars using
group vars.
I also removed several unnecessary definitions of
pip_lock_to_internal_repo in the playbooks since it is already
defined in the group_vars/all.yml.
Change-Id: Iddf27179d5babb91f4518202bdae5855f110b958
91e3de51f2