Remove incompatible definition of pop() from OrderingList (#229)

We can as well inherit the signature from list.

Author: JukkaL

sqlalchemy-stubs/ext/orderinglist.pyi

@@ -12,7 +12,6 @@ class OrderingList(list):
     def append(self, entity): ...
     def insert(self, index, entity): ...
     def remove(self, entity): ...
-    def pop(self, index: int = ...): ...
     def __setitem__(self, index, entity): ...
     def __delitem__(self, index): ...
     def __setslice__(self, start, end, values): ...