Do not use transactions when reading settings

There is no need to use database transactions to simply read settings.
We also were not setting the transaction as successful, which was
causing the outer transaction for the whole onUpgrade operation to be
rolled back, meaning that some devices would be stuck at old db
versions and perform repeated migration attempts on every boot.

Issue: calyxos#1290
Change-Id: Icefe994379152f9a3aa6c0c5b447cc55d5c4cf46