migrate leave foreignkey  out of consideration
The foreign keys are returned by `pragma foreign_key_list("...")`. I'm not sure I understand the issue you're describing.
I drop a field to a tabel ,but not I success. Finally, I found, it's a bug.
you create a tmp table and then, drop old tabel. BUT, leave foreignkey  out of consideration
`      
        # Find any foreign keys we may need to remove.

        self.database.get_foreign_keys(table)
`

do nothing
I used sqlite.
maybe I should use `PRAGMA foreign_keys=OFF` first