chore: drop Python2-specific aliases

Author: tseaver

tests/unit/test_bidi.py

@@ -221,18 +221,12 @@ def cancel_side_effect():
 
 
 class ClosedCall(object):
-    # NOTE: This is needed because defining `.next` on an **instance**
-    #       rather than the **class** will not be iterable in Python 2.
-    #       This is problematic since a `Mock` just sets members.
-
     def __init__(self, exception):
         self.exception = exception
 
     def __next__(self):
         raise self.exception
 
-    next = __next__  # Python 2
-
     def is_active(self):
         return False
 
@@ -354,8 +348,6 @@ def __next__(self):
             raise item
         return item
 
-    next = __next__  # Python 2
-
     def is_active(self):
         return self._is_active