Revert "Merge branch 'hierarchy_cache' of https://github.com/crhallberg/vufind"
(Pull request was merged due to accidental button press -- not ready yet).

This reverts commit c7fa81493cd5ab732cecaedfc90f35d60539478f, reversing
changes made to 1e3c293eb3b75ce542c069ae80f58733f3417bba.