Remove types exist action (#43344)

The types exists action was kept around only to not break transport 
client, as RestGetMappingAction has its own logic that ties into the
unified HEAD requests handling.

Now that tranport client is removed, we can remove also
TransportTypesExistsAction as well as its corresponding request,
request builder, response, and action.

Author: javanna

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

@@ -101,8 +101,6 @@
 import org.elasticsearch.action.admin.indices.create.TransportCreateIndexAction;
 import org.elasticsearch.action.admin.indices.delete.DeleteIndexAction;
 import org.elasticsearch.action.admin.indices.delete.TransportDeleteIndexAction;
-import org.elasticsearch.action.admin.indices.exists.types.TransportTypesExistsAction;
-import org.elasticsearch.action.admin.indices.exists.types.TypesExistsAction;
 import org.elasticsearch.action.admin.indices.flush.FlushAction;
 import org.elasticsearch.action.admin.indices.flush.SyncedFlushAction;
 import org.elasticsearch.action.admin.indices.flush.TransportFlushAction;
@@ -463,7 +461,6 @@ public <Request extends ActionRequest, Response extends ActionResponse> void reg
         actions.register(GetIndexAction.INSTANCE, TransportGetIndexAction.class);
         actions.register(OpenIndexAction.INSTANCE, TransportOpenIndexAction.class);
         actions.register(CloseIndexAction.INSTANCE, TransportCloseIndexAction.class);
-        actions.register(TypesExistsAction.INSTANCE, TransportTypesExistsAction.class);
         actions.register(GetMappingsAction.INSTANCE, TransportGetMappingsAction.class);
         actions.register(GetFieldMappingsAction.INSTANCE, TransportGetFieldMappingsAction.class,
                 TransportGetFieldMappingsIndexAction.class);