input: Write a python function to delete an item from a list if it exists.
  assert delete_item([1, 2, 3, 4, 5], 3) == [1, 2, 4, 5]
  assert delete_item([10, 20, 30, 40], 25) == [10, 20, 30, 40]
  assert delete_item(['a', 'b', 'c'], 'b') == ['a', 'c']
output: def delete_item(lst, item):
      if item in lst:
          lst.remove(item)
      return lst