input: Write a python function to remove duplicate elements from a list.
  assert remove_duplicates([1, 4, 2, 5, 6, 4, 1, 5]) == [1, 4, 2, 5, 6]
  assert remove_duplicates([10, 10, 20, 30, 40, 40]) == [10, 20, 30, 40]
  assert remove_duplicates([5, 3, 2, 2, 3, 5]) == [5, 3, 2]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))