Can we remove this library?

I took a look for existing stored entity data recently while looking at adding thrift round-trip tests. I can’t find any: there’s an entity index in CAPI that appears to be empty, and though it’s possible for some atoms (guides, timelines, profiles) to contain entities, CAPI searches via Cerebro suggest there are no existing atoms where those fields are non-null. Being optimistic, is there any chance there’s no such data and we could entirely remove this library?

## Tasks

- [ ] Define the list of tools that might hold data upstream from CAPI for this data type
- [ ] atoms
- atom workshop
- [ ] entities
- [ ] Verify there's no data for this data type in those tools
- [X] There are no stored atoms in atom workshop containing entities
- [X] No Profile atoms with entities
- [X] No Guide atoms with entities
- [X] No Timeline atoms with entities
- [ ] There are no entities stored upstream of CAPI (in places other than atoms)
- [ ] Verify there's no data held in CAPI for this data type
- [x] The entities index in CAPI is empty

Start by reviewing the CAPI entities index and the existing Cerebro searches, then investigate atom workshop for Profile, Guide, and Timeline atoms. Define all upstream tools that may store entities and verify each one, including storage outside atoms. Done means the data absence is established across those systems and the library-removal decision is supported.

Written by the indexing model from the issue text.