Removed unused imports.

src/main/java/org/gitlab4j/api/webhook/WebHookManager.java

@@ -8,7 +8,6 @@ import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import javax.servlet.http.HttpServletRequest;
-import javax.servlet.http.HttpUtils;
 
 import org.gitlab4j.api.GitLabApi;
 import org.gitlab4j.api.GitLabApiException;