remove venv support
remove venv support

edmorley/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,andela-brotich/wger-buildpack-python,benmurden/heroku-buildpack-python-ember,benmurden/heroku-buildpack-python-ember,AltSchool/heroku-buildpack-python,heroku/heroku-buildpack-python,ad-m/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,Scalingo/python-buildpack,ad-m/heroku-buildpack-python,skilljar/heroku-buildpack-python,Scalingo/python-buildpack,AltSchool/heroku-buildpack-python,heroku/heroku-buildpack-python,joshfriend/heroku-buildpack-python