Remove install_venv_common module

It recently came to light (at least to me) the venv scripts in
oslo-incubator.git are not the recommended way of creating a
virtual environment. With that in mind we remove it from cookiecutter.

Change-Id: I4f234e0d333cf42dbe0eaa76d54d3367e0dfec2a
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>
Merge "Remove install_venv_common module"