Once the old country schema is dropped (T408931), we can clean up the code: drop the migration flag and associated code, + misc clean-ups (e.g. make things not nullable in the code; drop temporary methods; make sure in-person/hybrid events have an Address object; perhaps add a getAddressOrThrow() for type safety that returns Address or throws; etc.)
Acceptance criteria
- Old compatibility code is dropped
- No change in functionality