input: Write a function to remove disconnected clients from the list of clients.
  assert list_of_clients == [client1, client2, client3]
  remove_disconnected_clients(client2)
  assert list_of_clients == [client1, client3]
  remove_disconnected_clients(client1)
  assert list_of_clients == [client3]
output: def remove_disconnected_clients(client):
      global list_of_clients
      if client in list_of_clients:
          list_of_clients.remove(client)