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