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, 10, 20, 30, 30, 40]) == [10, 20, 30, 40]
  assert remove_duplicates([5, 6, 7, 8, 9, 9, 8, 7, 6, 5]) == [5, 6, 7, 8, 9]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))