Slim down to just find with cursor in postgres
Slim down to just find with cursor in postgres

- Simplify since there were a number of problems in the extracted code
- If postgres, default to using cursors; otherwise, go back to native find_in_batches
- Get rid of switchman shard activations
- Get rid of exclusive scope.  Couldn't get klass.send(:with_exclusive_scope) to work
- Removed ability to include relation associations
- Return batch; implementation was returning connection

instructure/ar_find_in_batches_with_usefulness