[DOCS] delete by query requires a top-level query parameter

Closes #5044
(cherry picked from commit 1e265b3)

docs/reference/docs/delete-by-query.asciidoc

@@ -12,7 +12,9 @@ body. Here is an example:
 $ curl -XDELETE 'http://localhost:9200/twitter/tweet/_query?q=user:kimchy'
 
 $ curl -XDELETE 'http://localhost:9200/twitter/tweet/_query' -d '{
-    "term" : { "user" : "kimchy" }
+    "query" : {
+        "term" : { "user" : "kimchy" }
+    }
 }
 '
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