Remove deprecated _suggest endpoint (#22203)

In #20305, _suggest endpoint was deprecated
in favour of using _search endpoint. This
commit removes the dedicated _suggest endpoint
entirely from master.

core/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -310,7 +310,6 @@
 import org.elasticsearch.rest.action.search.RestMultiSearchAction;
 import org.elasticsearch.rest.action.search.RestSearchAction;
 import org.elasticsearch.rest.action.search.RestSearchScrollAction;
-import org.elasticsearch.rest.action.search.RestSuggestAction;
 import org.elasticsearch.threadpool.ThreadPool;
 
 import static java.util.Collections.unmodifiableList;
@@ -550,7 +549,6 @@ static Set<Class<? extends RestHandler>> setupRestHandlers(List<ActionPlugin> ac
         registerRestHandler(handlers, RestMultiGetAction.class);
         registerRestHandler(handlers, RestDeleteAction.class);
         registerRestHandler(handlers, org.elasticsearch.rest.action.document.RestCountAction.class);
-        registerRestHandler(handlers, RestSuggestAction.class);
         registerRestHandler(handlers, RestTermVectorsAction.class);
         registerRestHandler(handlers, RestMultiTermVectorsAction.class);
         registerRestHandler(handlers, RestBulkAction.class);

core/src/main/java/org/elasticsearch/search/suggest/Suggest.java

@@ -150,18 +150,10 @@ public void writeTo(StreamOutput out) throws IOException {
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject(NAME);
-        toInnerXContent(builder, params);
-        builder.endObject();
-        return builder;
-    }
-
-    /**
-     * use to write suggestion entries without <code>NAME</code> object
-     */
-    public XContentBuilder toInnerXContent(XContentBuilder builder, Params params) throws IOException {
         for (Suggestion<?> suggestion : suggestions) {
             suggestion.toXContent(builder, params);
         }
+        builder.endObject();
         return builder;
     }
 

rest-api-spec/src/main/resources/rest-api-spec/test/suggest/10_basic.yaml

@@ -24,19 +24,3 @@ setup:
   - match: {suggest.test_suggestion.1.options.0.text: amsterdam}
   - match: {suggest.test_suggestion.2.options.0.text: meetup}
 
----
-"Suggest API should have deprecation warning":
-  - skip:
-      features: 'warnings'
-  - do:
-      warnings:
-        - "[POST /_suggest] is deprecated! Use [POST /_search] instead."
-      suggest:
-        body:
-          test_suggestion:
-            text: "The Amsterdma meetpu"
-            term:
-              field: body
-
-  - match: {test_suggestion.1.options.0.text: amsterdam}
-  - match: {test_suggestion.2.options.0.text: meetup}