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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def unregister_callback(callback_id):
 """unregister a callback registration"""

    global _callbacks
    obj = _callbacks.pop(callback_id, None)
    threads = []
    if obj is not None:
        t, quit = obj
        quit.set()
        threads.append(t)
    for t in threads:
        t.join()