Remove mentions of doc_type in Mapping documentation

Author: sethmlarson

docs/api.rst

@@ -53,7 +53,7 @@ pattern to the query dsl:
     from elasticsearch_dsl import Keyword, Mapping, Nested, Text
 
     # name your type
-    m = Mapping('my-type')
+    m = Mapping()
 
     # add fields
     m.field('title', 'text')
@@ -93,7 +93,7 @@ directly from an existing type:
 .. code:: python
 
     # get the mapping from our production cluster
-    m = Mapping.from_es('my-index', 'my-type', using='prod')
+    m = Mapping.from_es('my-index', using='prod')
 
     # update based on data in QA cluster
     m.update_from_es('my-index', using='qa')