input: Write a function to delete the last element of a list.
  assert delete_last([1, 2, 3, 4, 5]) == [1, 2, 3, 4]
  assert delete_last(['a', 'b', 'c', 'd']) == ['a', 'b', 'c']
  assert delete_last([10, 20, 30]) == [10, 20]
output: def delete_last(lst):
      if lst:
          lst.pop()
      return lst