Drop transfers before populating new ones

trainvel/gtfs/management/commands/update_trainvel_gtfs.py

@@ -368,6 +368,7 @@ class Command(BaseCommand):
             stop_times.clear()
 
         if os.path.exists(os.path.join(zip_dir, "transfers.txt")):
+            Transfer.objects.filter(Q(from_stop__gtfs_feed_id=gtfs_code) | Q(to_stop__gtfs_feed_id=gtfs_code)).delete()
             transfers = []
             for transfer_dict in read_csv("transfers.txt"):
                 transfer_dict: dict