This code was originally located at:
./openedx/core/djangoapps/coursegraph
However, code makes more sense within the ./cms tree, because:
* it is responsible for publishing course content to an
external system, with is within the responsibilities of CMS, and
* is uses modulestore, which is discouraged for use in LMS
(see 0011-limit-modulestore-use-in-lms.rst).
So, we move the code to:
./cms/djangoapps/coursegraph
and uninstall coursegraph from LMS.
We do not expect this refactor to have any breaking downstream effects.
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