At one point, we envisioned having different kinds of libraries, e.g.
a "Video" library would be distinct from a "Problem" library. Later on,
we decided on a more generalized form of Libraries, where any given
library can hold any combination of content–which would then be
organized using collections and tagging.
Due to this shift in perspective, these values haven't actually been
used for a long time. This is just getting rid of them altogether.
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