chore(RetryDownloadingEventListener): remove an unused import.

Correction for 858a074 commit.

Author: php-coder

src/main/java/ru/mystamps/web/feature/series/importing/event/RetryDownloadingEventListener.java

@@ -18,7 +18,6 @@
 package ru.mystamps.web.feature.series.importing.event;
 
 import lombok.RequiredArgsConstructor;
-import org.apache.commons.lang3.Validate;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.context.ApplicationEventPublisher;