* Remove full table scan of VerificationDeadline.
Before this commit, we were doing a full table scan of
student_verificationdeadline, loading the results into a giant
dict, and reading/writing that to the cache. This was fine when the
code was introduced and there were dozens of courses, but now that
we're over 12K courses, it's becoming a major performance issue for
the Student Dashboard.
This uses a subquery to the course enrollment table so that we're
only ever pulling back the deadlines to a student's enrolled courses
for any given request. It removes the cache access entirely.
a712f1f93b