This code is necessary for queries passed to the server as legacy OP_QUERY find. Since we are removing support for OP_QUERY find, SPLIT_LIMITED_SORT can (eventually) be deleted.

We suspect that this code deletion cannot be done until after we release 6.0 in order to ensure that the 5.0/5.1 upgrade/downgrade continues to function as expected. In particular, a 5.0 mongos could receive an OP_QUERY find with ntoreturn, and forward this request to the shards as an OP_MSG find command with ntoreturn. This find command may require SPLIT_LIMITED_SORT to work. If this is correct, then the ticket should be scheduled post-6.0 alongside tasks such as SERVER-57384.