[skip ci] remove doc entries related to < 7.x

Author: jsvd

docs/index.asciidoc

@@ -610,8 +610,7 @@ Elasticsearch with the same ID.
 
 NOTE: This option is deprecated due to the
 https://www.elastic.co/guide/en/elasticsearch/reference/6.0/removal-of-types.html[removal
-of types in Elasticsearch 6.0]. It will be removed in the next major version of
-Logstash.
+of types in Elasticsearch 6.0].
 
 NOTE: This value is ignored and has no effect for Elasticsearch clusters `8.x`.
 
@@ -620,9 +619,7 @@ similar events to the same 'type'. String expansion `%{foo}` works here.
 If you don't set a value for this option:
 
 - for elasticsearch clusters 8.x: no value will be used;
-- for elasticsearch clusters 7.x: the value of '_doc' will be used;
-- for elasticsearch clusters 6.x: the value of 'doc' will be used;
-- for elasticsearch clusters 5.x and below: the event's 'type' field will be used, if the field is not present the value of 'doc' will be used.
+- for elasticsearch clusters 7.x: the value of '_doc' will be used.
 
 [id="plugins-{type}s-{plugin}-ecs_compatibility"]
 ===== `ecs_compatibility`
@@ -1037,8 +1034,6 @@ NOTE: Deprecates <<plugins-{type}s-{plugin}-failure_type_logging_whitelist>>.
 
 This setting asks Elasticsearch for the list of all cluster nodes and adds them
 to the hosts list.
-For Elasticsearch 5.x and 6.x any nodes with `http.enabled` (on by default) will
-be added to the hosts list, excluding master-only nodes.
 
 [id="plugins-{type}s-{plugin}-sniffing_delay"]
 ===== `sniffing_delay`