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.
Remove the local_infile setting as it is MySQL specific
Remove the config block for the production database

- The whole file is overwritten on deploy, so it's confusing for those
  of us looking at the checked out database config and it not being the
  same as production.
Merge pull request #443 from alphagov/remove_synchronus_commit_setting_from_dev

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