Remove check from category-structure that all categories are non-empty and all tasks are used
requested to merge lemberger/competition-scripts:make-check-categories-not-handle-set-files into main
This should be a part of the check-benchdefs, not category structure, but must be implemented differently than this.
We do not want the category structure to directly reason about the benchmark task files and set files; for the category structure, the benchmark definitions should be the source of truth.