[JENKINS-28683] Fix unit test and remove unised import.

test/src/test/java/hudson/model/APeriodicWorkTest.java

@@ -23,7 +23,7 @@ public class APeriodicWorkTest {
     public void newExtensionsAreScheduled() throws Exception {
         TestAperiodicWork tapw = new TestAperiodicWork();
 
-        int size = PeriodicWork.all().size();
+        int size = AperiodicWork.all().size();
         ExtensionList.lookup(AperiodicWork.class).add(tapw);
 
         assertThat("we have one new AperiodicWork", AperiodicWork.all(), hasSize(size+1));

test/src/test/java/hudson/model/PeriodicWorkTest.java

@@ -2,7 +2,6 @@ package hudson.model;
 
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
 
 import org.junit.Rule;
 import org.junit.Test;