refactor: remove dead DATA_STREAM_COMPATIBLE_ES_VERSION check

With CONNECTOR_V11_COMPATIBLE_ES_VERSION raised to 8.0.0, any cluster
that passes the version gate trivially satisfies the old 7.9.0
data-stream floor. The branch could never fire; remove the constant
and the guarded block.

Author: yeikel

src/main/java/io/confluent/connect/elasticsearch/Validator.java

@@ -76,7 +76,6 @@ public class Validator {
   private static final Logger log = LoggerFactory.getLogger(Validator.class);
 
   private static final String CONNECTOR_V11_COMPATIBLE_ES_VERSION = "8.0.0";
-  private static final String DATA_STREAM_COMPATIBLE_ES_VERSION = "7.9.0";
 
   public static final String EXTERNAL_RESOURCE_CONFIG_TOGETHER_ERROR =
           String.format("Invalid configuration:"
@@ -459,18 +458,6 @@ private void validateVersion(ElasticsearchClient client) {
       // ElasticsearchException.
       return;
     }
-    if (config.isDataStream()
-        && compareVersions(esVersionNumber, DATA_STREAM_COMPATIBLE_ES_VERSION) < 0) {
-      String errorMessage = String.format(
-          "Elasticsearch version %s is not compatible with data streams. Elasticsearch"
-              + "version must be at least %s.",
-          esVersionNumber,
-          DATA_STREAM_COMPATIBLE_ES_VERSION
-      );
-      addErrorMessage(CONNECTION_URL_CONFIG, errorMessage);
-      addErrorMessage(DATA_STREAM_TYPE_CONFIG, errorMessage);
-      addErrorMessage(DATA_STREAM_DATASET_CONFIG, errorMessage);
-    }
     if (compareVersions(esVersionNumber, CONNECTOR_V11_COMPATIBLE_ES_VERSION) < 0) {
       String errorMessage = String.format(
           "Connector version %s is not compatible with Elasticsearch version %s. Elasticsearch "