Fix entrypoint.sh / docker-compose up. (#4747)

We no longer use virtualenv; we just install our Python dependencies
globally.

test/entrypoint.sh

@@ -53,10 +53,6 @@ if [ -n "${PKCS11_PROXY_SOCKET:-}" ]; then
 fi
 
 if [[ $# -eq 0 ]]; then
-    # the activate script touches PS1, which is undefined, so we have to relax
-    # the "fail on undefined" setting here.
-    set +u
-    source ${CERTBOT_PATH:-/certbot}/${VENV_NAME:-venv3}/bin/activate
     exec python3 ./start.py
 fi