Issue #22609: Revert changes in UserDict. They conflicted with existing tests.

Lib/collections/__init__.py

@@ -893,14 +893,7 @@ class ChainMap(MutableMapping):
 class UserDict(MutableMapping):
 
     # Start by filling-out the abstract methods
-    def __init__(*args, **kwargs):
-        if not args:
-            raise TypeError("descriptor '__init__' of 'UserDict' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
-        dict = args[0] if args else None
+    def __init__(self, dict=None, **kwargs):
         self.data = {}
         if dict is not None:
             self.update(dict)