Avoid batch S3 deletes in builder

tests/test_template_init.py

@@ -192,9 +192,11 @@ class _FakeS3:
     ) -> None:
         self.objects[Key] = bytes(Body)
 
+    def delete_object(self, *, Bucket: str, Key: str) -> None:
+        self.objects.pop(Key, None)
+
     def delete_objects(self, *, Bucket: str, Delete: dict[str, object]) -> None:
-        for obj in Delete["Objects"]:  # type: ignore[index]
-            self.objects.pop(obj["Key"], None)
+        raise AssertionError("batch DeleteObjects should not be used")
 
 
 class _FakePaginator: