input: Write a python function to return a list of unique elements from the input list.
  assert unique_list([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert unique_list([1, 1, 1, 1]) == [1]
  assert unique_list([5, 6, 7, 8, 8, 7, 6, 5]) == [5, 6, 7, 8]
output: def unique_list(input_list):
      return list(set(input_list))