fix MapDataset creation in python 3.9

Summary:
fix facebookresearch#3405

The old code works for python 3.6 & 3.7; fails for python 3.9

Reviewed By: zhanghang1989

Differential Revision: D30599139

fbshipit-source-id: ab9e5d68387b68e1095112e9c2531a971567accc

Author: ppwwyyxx

detectron2/data/common.py

@@ -74,7 +74,7 @@ def __new__(cls, dataset, map_func):
         if is_iterable:
             return _MapIterableDataset(dataset, map_func)
         else:
-            return super().__new__(cls, dataset, map_func)
+            return super().__new__(cls)
 
     def __getnewargs__(self):
         return self._dataset, self._map_func