Support the SingleRemove flag in OP_DELETE for pre-2.6 servers

This is needed to support the bulk API removeOne method when connected to pre-2.6 versions of MongoDB. A new parameter should be added to the existing remove method, named "multi" to match the update method. When set to true (the default) remove will keep its current behavior of removing all documents that match the query criteria. When set to false only the first matching document is removed. The server behavior is configured through the SingleRemove option of OP_DELETE:

http://docs.mongodb.org/meta-driver/latest/legacy/mongodb-wire-protocol/#op-delete

If your driver already supports this behavior, regardless of existing parameter name, no changes are required. Just validate this ticket.