input: Write a function to delete duplicates from a list.
  assert delete_duplicates([1, 2, 3, 2, 4, 1]) == [1, 2, 3, 4]
  assert delete_duplicates([5, 5, 5, 5]) == [5]
  assert delete_duplicates([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def delete_duplicates(lst):
      return list(dict.fromkeys(lst))