Removes use of prefer_v2_templates (#66316) (#66347)

prefer_v2_templates is no longer an accepted query parameter. V2 templates are now preferred by default.

Signed-off-by: Tyler Smalley <[email protected]>

Author: Tyler Smalley

x-pack/test/functional/es_archives/endpoint/policy/mappings.json

@@ -499,7 +499,6 @@
         },
         "number_of_replicas": "1",
         "number_of_shards": "1",
-        "prefer_v2_templates": "true",
         "query": {
           "default_field": [
             "message"

x-pack/test/functional/es_archives/reporting/archived_reports/mappings.json

@@ -100,8 +100,7 @@
       "index": {
         "auto_expand_replicas": "0-1",
         "number_of_replicas": "0",
-        "number_of_shards": "1",
-        "prefer_v2_templates": "false"
+        "number_of_shards": "1"
       }
     }
   }