For name and description, we'll derive these from the role_field and
content type, which is much better for lots of reasons (eg changing text
the future). Also ditched the rest of the fields comming from the
standard common base model, we didn't use them and they cost several
indexes on the table.
We have some signal handlers now that perform work that do work
automatically that we want to explicitly test in our migration path, so
we have to undo some things in order to test the migration code.
