Do not try to recreate test_owner/test_app_owner roles

The `DROP ROLE` might cause an issue when there's already other database
with objects that depend on the role. `DROP OWNED` can only drop objects
in the current database. Any dependent object in other databases will
still be present and will cause `DROP ROLE` to fail. This might be the
case after a failed test that uses that role, as databases are dropped
only for successful runs.
This will not play well for running multiple tests using the same role.
The second test won't be able to drop the role, because the first one
likely already created some objects that depend on that role.
Also, each test is run is a separate database cloned from the current
`block_log` database, so there shouldn't be the need to remove objects
in the current database.