Elastic query: remove matching on document type.

ElasticSearch 6 removes support for different document types in one index,
so we don't have to match for it any more. Furthermore, elasticsearch_dsl
seems to save with the generic 'doc' type, so this check is
counter-productive.

pillar/api/search/queries.py

@@ -72,9 +72,7 @@ def do_node_search(query: str, terms: dict, page: int) -> dict:
         Q('term', tags=query),
     ]
 
-    must = [
-        Q('term', _type='node')
-    ]
+    must = []
 
     if not query:
         should = []