input: Write a python function to remove duplicates from a list.
  assert remove_duplicates([3, 5, 7, 9, 3, 5, 7]) == [3, 5, 7, 9]
  assert remove_duplicates([1, 1, 1, 1, 1]) == [1]
  assert remove_duplicates([2, 4, 6, 8, 2, 4, 6]) == [2, 4, 6, 8]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))