Remove bok-choy usage

[salman2013]

This repo's tests still use the bok-choy framework, which openedx/public-engineering#13. The bok-choy repository is no longer being maintained, and it will soon be archived.

Once the bok-choy repo is archived, the tests should continue working, as we will not be removing the package's releases from PyPI. For long-term maintainability of this repo, though, the tests should eventually be upgraded to a non-bok-choy testing framework or removed.

[feanil]

#66 was merged to remove this usage.