This reverts commit a7fa0c21.

Sass compilation is no longer dependent on Ruby, so we are
removing its dependencies.

Other small changes:
* output the list of installed python packages
* tee the pylint output to the console so the build doesn't timeout when computing violations

CircleCI re-uses your existing venv cache.  If we don't do this, it will prompt the user for what to do and hang the build on certain kinds of updates.