doc_type is gone. 2.3.7 changes many function signatures because opensearch-py did

[Matthew Martin]

Opensearch-py phased out doc_type. Since it doesn't exist anymore, the fakes can't meaningfully support its old behavior. This process was going on in Elasticsearch-land too.

This I think is the first change I've made to the library that has any risk of breaking someone's build, so I'm noting it here in the issues.