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