Frames used in migrations

"frames" reflect the current data model, which can change, whereas database migrations operate on historic models which should be fixed to the specific migration.

### Observed

```
$ git grep frames -- lib/model/migrations/
lib/model/migrations/20200220-01-repair-submission-parsing.js:const { Submission } = require('../frames');
lib/model/migrations/20210120-01-instance-names.js:const { Submission } = require('../frames');
lib/model/migrations/20211008-01-track-select-many-options.js:const { Form } = require('../frames');
```

### Expected

Migrations should not rely on application code for their understanding of the database schema.