elasticsearch: Remove the deprecated document type

According to the removal-of-types[1] documentation, it is no longer
necessary to specify a document type.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/7.17/removal-of-types.html

Change-Id: I02996ce328a48b5ae6493646abe08ebab31ec962

zuul/driver/elasticsearch/connection.py

@@ -113,7 +113,6 @@ class ElasticsearchConnection(BaseConnection):
             source['@timestamp'] = datetime.utcfromtimestamp(
                 int(source['start_time'])).strftime("%Y-%m-%dT%H:%M:%S.%fZ")
             d['_index'] = index
-            d['_type'] = 'zuul'
             d['_op_type'] = 'index'
             d['_source'] = source
             yield d