fix checkstyle

Author: abh1sar

server/src/test/java/com/cloud/vm/snapshot/VMSnapshotManagerTest.java

@@ -68,7 +68,6 @@
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
-import org.mockito.ArgumentMatchers;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 import org.mockito.Spy;