storagebackends takes ids on delete

src/main/java/org/gcube/data/access/storagehub/storage/backend/impl/GCubeStorageBackend.java

@@ -64,10 +64,10 @@ public class GCubeStorageBackend implements StorageBackend {
 	}
 	
 	@Override
-	public void onDelete(Content content) {
+	public void onDelete(String id) {
 		log.debug("deleting");
 		IClient storageClient = getStorageClient(AuthorizationProvider.instance.get().getClient().getId()).getClient();
-		storageClient.remove().RFileById(content.getStorageId());
+		storageClient.remove().RFileById(id);
 	}
 	
 	private static StorageClient getStorageClient(String login){