Merge pull request #3113 from certbot/revert-2936-dev-venv-fix

Revert "Use --force-reinstall to fix bad virtualenv package"

tools/_venv_common.sh

@@ -18,8 +18,7 @@ virtualenv --no-site-packages $VENV_NAME $VENV_ARGS
 # Separately install setuptools and pip to make sure following
 # invocations use latest
 pip install -U setuptools
-# --force-reinstall used to fix broken pip installation on some systems
-pip install --force-reinstall -U pip
+pip install -U pip
 pip install "$@"
 
 set +x