input: Write a python function to remove duplicates from a list.
  assert remove_duplicates([1, 2, 3, 4, 3, 2]) == [1, 2, 3, 4]
  assert remove_duplicates([1, 1, 1, 1]) == [1]
  assert remove_duplicates([5, 6, 7, 5, 6, 8]) == [5, 6, 7, 8]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))