Revert "SessionRepository.save returns S"

See gh-809

spring-session-jdbc/src/main/java/org/springframework/session/jdbc/JdbcOperationsSessionRepository.java

@@ -371,7 +371,7 @@ public class JdbcOperationsSessionRepository implements
 		return session;
 	}
 
-	public JdbcSession save(final JdbcSession session) {
+	public void save(final JdbcSession session) {
 		if (session.isNew()) {
 			this.transactionOperations.execute(new TransactionCallbackWithoutResult() {
 
@@ -458,7 +458,6 @@ public class JdbcOperationsSessionRepository implements
 			});
 		}
 		session.clearChangeFlags();
-		return session;
 	}
 
 	public JdbcSession findById(final String id) {