Remove manual sections panopticon integration

Now that manuals are stored and fetch from Content Store instead of Content API, we don't need to register artefacts with Panopticon for them.

The benefit of removing this integration is to remove unnecessary code and to speed up publishing manuals by removing a lot of API calls. In the case of the Family Procedure Rules this removes one hundred and eleven (111!) calls to Panopticon which take around 1–4s each to complete.

The main commit of interest here is 251be1b. 01c1442 is just a minor refactoring simplification.