Remove use of find in batches

When passed an `ActiveRecord::Relation` with `order` or `limit` set, [ActiveRecord::Relation#find_in_batches](http://api.rubyonrails.org/classes/ActiveRecord/Batches.html#method-i-find_in_batches) will ignore either.

This PR removes the use of `ActiveRecord::Relation#find_in_batches` in favor of `Enumerable#each_slice` during batch caching.