Support Nook HD and HD+: use journal_mode delete

The Nook HD and Nook HD+ have issues changing from a journal_mode of WAL to one of DELETE, which rendered them unable to use AnkiDroid. This addresses the issue by always using mode DELETE on those devices, which is preferable to not being able to use AnkiDroid at all. It may be possible to properly use WAL journal_mode on those devices, but a reliable way to convert to mode DELETE from mode WAL would need to be found.