builder: Install butterfly system-wide

builder/test/tests.sh

@@ -27,10 +27,7 @@ tcpdump --version
 monkey --version
 pigpiod -v
 i2cdetect -V
-# butterfly uses its own venv, so we honor that
-. /root/butterfly_env/bin/activate
 butterfly -h
-# deactivate venv as needed
 deactivate
 espeak --version
 mjpg_streamer --version