Fix Checkstyle violations

https://build.spring.io/browse/INT-SI43X-244/

Author: artembilan

spring-integration-jdbc/src/test/java/org/springframework/integration/jdbc/JdbcMessageStoreChannelOnePollerIntegrationTests.java

@@ -41,8 +41,6 @@
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 import org.springframework.transaction.PlatformTransactionManager;
-import org.springframework.transaction.TransactionStatus;
-import org.springframework.transaction.support.TransactionCallback;
 import org.springframework.transaction.support.TransactionTemplate;
 import org.springframework.util.StopWatch;