Fix checkstyle violation

Author: rstoyanchev

spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java

@@ -52,7 +52,6 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;