Remove unused import

See gh-22543

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestMappingHandlerMapping.java

@@ -23,7 +23,6 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 
 import org.springframework.context.EmbeddedValueResolverAware;
 import org.springframework.core.annotation.AnnotatedElementUtils;