Polish "Improve Spring Session sample"

Closes gh-10351

Author: snicoll

spring-boot-samples/spring-boot-sample-session/src/main/java/sample/session/HelloRestController.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package sample.session.redis;
+package sample.session;
 
 import java.util.UUID;
 

spring-boot-samples/spring-boot-sample-session/src/main/java/sample/session/SampleSessionApplication.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package sample.session.redis;
+package sample.session;
 
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;

spring-boot-samples/spring-boot-sample-session/src/test/java/sample/session/SampleSessionApplicationTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package sample.session.redis;
+package sample.session;
 
 import java.net.URI;