fix build error AlertManagerImplTest

Author: weizhouapache

server/src/test/java/com/cloud/alert/AlertManagerImplTest.java

@@ -56,12 +56,6 @@
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.verify;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
-import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.Mockito.verify;
-
 @RunWith(MockitoJUnitRunner.class)
 public class AlertManagerImplTest {