fix code style

Author: osulzhenko

src/test/java/org/prebid/server/bidder/insticator/InsticatorBidderTest.java

@@ -45,7 +45,6 @@
 import static java.util.function.UnaryOperator.identity;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
-import static org.assertj.core.api.InstanceOfAssertFactories.COLLECTION;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.BDDMockito.given;