CategoryServiceImpl: remove unused import.

Fix warning from PMD/CheckStyle.

Correction for dcffa75 commit.

No functional changes.

Author: php-coder

src/main/java/ru/mystamps/web/service/CategoryServiceImpl.java

@@ -33,7 +33,6 @@
 
 import ru.mystamps.web.dao.JdbcCategoryDao;
 import ru.mystamps.web.dao.dto.AddCategoryDbDto;
-import ru.mystamps.web.entity.Category;
 import ru.mystamps.web.entity.Collection;
 import ru.mystamps.web.entity.User;
 import ru.mystamps.web.service.dto.AddCategoryDto;