The CourseQualityView used to call edx-val's get_video_for_course(),
which would return a fully serialized data structure that included all
encodings and inefficiently serialized them with many n+1 queries. This
is tolerable in a paginated web view, but not when pulling all of a
large courses's videos at once.
Making this change collapsed the number of queries for a large sample
MIT course from over 3000 down to 1.
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