input: Write a python function to remove duplicate elements from a list.
  assert remove_duplicates([1, 2, 2, 3, 4, 4, 5])==[1, 2, 3, 4, 5]
  assert remove_duplicates([10, 20, 20, 30, 40, 50, 50, 60])==[10, 20, 30, 40, 50, 60]
  assert remove_duplicates(['a', 'b', 'b', 'c', 'd', 'd', 'e'])==['a', 'b', 'c', 'd', 'e']
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))