docs: remove reference to returning clauses for Batch DML (#2644)

* docs: remove reference to returning clauses for Batch DML

Remove the reference to THEN RETURN / RETURNING clauses for Batch DML
requests, as these clauses are ignored for batch DML and not returned to
the client.

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README.md

@@ -57,13 +57,13 @@ implementation 'com.google.cloud:google-cloud-spanner'
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-spanner:6.47.0'
+implementation 'com.google.cloud:google-cloud-spanner:6.48.0'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.47.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.48.0"
 ```
 <!-- {x-version-update-end} -->
 
@@ -431,7 +431,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-spanner/java11.html
 [stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-spanner.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.47.0
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.48.0
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

google-cloud-spanner/src/main/java/com/google/cloud/spanner/TransactionContext.java

@@ -162,11 +162,10 @@ default ResultSet analyzeUpdateStatement(
   }
 
   /**
-   * Executes a list of DML statements (which can include simple DML statements or DML statements
-   * with returning clause) in a single request. The statements will be executed in order and the
-   * semantics is the same as if each statement is executed by {@code executeUpdate} in a loop. This
-   * method returns an array of long integers, each representing the number of rows modified by each
-   * statement.
+   * Executes a list of DML statements in a single request. The statements will be executed in order
+   * and the semantics is the same as if each statement is executed by {@code executeUpdate} in a
+   * loop. This method returns an array of long integers, each representing the number of rows
+   * modified by each statement.
    *
    * <p>If an individual statement fails, execution stops and a {@code SpannerBatchUpdateException}
    * is returned, which includes the error and the number of rows affected by the statements that