input: Write a python function to remove duplicates from a list.
  assert unique_list([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert unique_list([10, 20, 10, 30, 20, 40]) == [10, 20, 30, 40]
  assert unique_list([7, 7, 7, 7, 7]) == [7]
output: def unique_list(lst):
      return list(dict.fromkeys(lst))