Removed F.__deepcopy__()

The method didn't change standard __deepcopy__ in any way.

django/db/models/expressions.py

@@ -138,11 +138,6 @@ class F(ExpressionNode):
         super(F, self).__init__(None, None, False)
         self.name = name
 
-    def __deepcopy__(self, memodict):
-        obj = super(F, self).__deepcopy__(memodict)
-        obj.name = self.name
-        return obj
-
     def prepare(self, evaluator, query, allow_joins):
         return evaluator.prepare_leaf(self, query, allow_joins)