Revert "move trigger tests to top-level x-pack test directory"

This reverts commit elastic/x-pack@1615d496d5.

Original commit: elastic/x-pack-elasticsearch@bcc2ae8e26

elasticsearch/x-pack/watcher/src/test/java/org/elasticsearch/xpack/trigger/schedule/engine/BaseTriggerEngineTestCase.java

@@ -26,6 +26,8 @@ import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
+import static org.elasticsearch.xpack.trigger.schedule.Schedules.hourly;
+import static org.elasticsearch.xpack.trigger.schedule.Schedules.interval;
 import static org.hamcrest.Matchers.is;
 import static org.joda.time.DateTimeZone.UTC;