Be consistent with production: don't set synchronous_commit in dev

- This was used for Postgres in dev for some reasons, but isn't set in production, and we should have no disparity between production and dev anymore. Remove it from the test database config as well for good measure.
This whole production block doesn't need to be here, actually - it suggests that these are the production settings, and they're not (and we don't want to have to remember to keep these up-to-date with the real production ones).