docs(opensearch): remove elasticsearch successor text (#23252)

Elastic has requested that we remove all "successor to Elasticsearch" text from our docs for legal reasons.
----

They have pointed out these two files specifically that they need us to change.

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Author: lizsnyder

packages/@aws-cdk/aws-elasticsearch/README.md

@@ -11,7 +11,7 @@
 
 <!--END STABILITY BANNER-->
 
-> Amazon Elasticsearch Service has been renamed to Amazon OpenSearch Service; consequently, the [@aws-cdk/aws-opensearchservice](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-opensearchservice-readme.html) module should be used instead. See [Amazon OpenSearch Service FAQs](https://aws.amazon.com/opensearch-service/faqs/#Name_change) for details. See [Migrating to OpenSearch](#migrating-to-opensearch) for migration instructions.
+> Instead of this module, we recommend using the [@aws-cdk/aws-opensearchservice](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-opensearchservice-readme.html) module. See [Amazon OpenSearch Service FAQs](https://aws.amazon.com/opensearch-service/faqs/#Name_change) for details. See [Migrating to OpenSearch](#migrating-to-opensearch) for migration instructions.
 
 ## Quick start
 

packages/@aws-cdk/aws-opensearchservice/README.md

@@ -22,8 +22,6 @@ Higher level constructs for Domain | ![Stable](https://img.shields.io/badge/stab
 
 <!--END STABILITY BANNER-->
 
-Amazon OpenSearch Service is the successor to Amazon Elasticsearch Service.
-
 See [Migrating to OpenSearch](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-elasticsearch-readme.html#migrating-to-opensearch) for migration instructions from `@aws-cdk/aws-elasticsearch` to this module, `@aws-cdk/aws-opensearchservice`.
 
 ## Quick start