input: Write a python function to remove duplicates from a list.
  assert remove_duplicates([1, 2, 2, 3]) == [1, 2, 3]
  assert remove_duplicates([4, 5, 5, 4, 6, 7, 7, 8]) == [4, 5, 6, 7, 8]
  assert remove_duplicates([10, 10, 10, 10]) == [10]
  assert remove_duplicates([]) == []
  assert remove_duplicates([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))