input: Write a python function to remove duplicates from a list.
  assert remove_duplicates([1, 2, 4, 5, 6, 2, 7, 4]) == [1, 2, 4, 5, 6, 7]
  assert remove_duplicates([10, 10, 20, 30, 40, 40, 50]) == [10, 20, 30, 40, 50]
  assert remove_duplicates([5, 5, 5, 5, 5, 5, 5]) == [5]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))