Remove extra useless parameter from RationalTime.__copy__ method

[JeanChristopheMorinPerso]

I noticed that the RationalTime.__copy__ method had an argument that is not used. The __copy__ special method is not supposed to accept arguments.

From https://docs.python.org/3/library/copy.html:

In order for a class to define its own copy implementation, it can define special methods __copy__() and __deepcopy__(). The former is called to implement the shallow copy operation; no additional arguments are passed. The latter is called to implement the deep copy operation; it is passed one argument, the memo dictionary.

[jminor]

Does __deepcopy__ have the same issue?
(edit) never mind, I see that the optional "memo" argument.