[topgen] Fix flake warning

Signed-off-by: Amaury Pouly <[email protected]>

util/topgen.py

@@ -14,7 +14,7 @@
 from io import StringIO
 from itertools import chain
 from pathlib import Path
-from typing import Dict, List, Optional, Tuple
+from typing import Dict, List
 
 import hjson
 import tlgen