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