Remove redundant section about setting up venv from quick-start
Remove redundant section about setting up venv from quick-start

There is no need to set up venv before we use tox. So we remove
the redundant section about setting up venv from quick-start.

Change-Id: I360d5c589dd31520721a5e5db3f24c7cc368e612
Closes-Bug: #1478767

paulczar/magnum,Tennyson53/magnum,openstack/magnum,Tennyson53/SUR,jay-lau/magnum,mjbrewer/testindex,eshijia/magnum,ramielrowe/magnum,sajuptpm/magnum,annegentle/magnum,ddepaoli3/magnum,annegentle/magnum,ChengTiesheng/magnum,dimtruck/magnum,eshijia/SUR,ChengTiesheng/magnum,ArchiFleKs/magnum,dimtruck/magnum,Tennyson53/magnum,sajuptpm/magnum,paulczar/magnum,ffantast/magnum,eshijia/magnum,mjbrewer/testindex,Alzon/SUR,ramielrowe/magnum,openstack/magnum,ArchiFleKs/magnum,Alzon/SUR,ffantast/magnum,mjbrewer/testindex,ddepaoli3/magnum,eshijia/SUR,Tennyson53/SUR