Fix Checkstyle violations

https://build.spring.io/browse/INT-SI43X-227

Author: artembilan

spring-integration-jdbc/src/test/java/org/springframework/integration/jdbc/lock/JdbcLockRegistryTests.java

@@ -26,7 +26,6 @@
 import static org.junit.Assert.assertTrue;
 
 import java.util.Map;
-import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;