input: Write a function to remove all instances of a specified item from a given list. If the given list is empty then return the empty list.
  assert remove_item([1, 2, 3, 4, 2, 5, 2], 2)==[1, 3, 4, 5]
  assert remove_item([3, 5, 2, 2, 7, 2, 9], 2)==[3, 5, 7, 9]
  assert remove_item([4, 3, 3, 4, 4, 4], 3)==[4, 4, 4, 4]
  assert remove_item([], 2)==[]
  assert remove_item([1, 2, 3, 2, 4, 2], 5)==[1, 2, 3, 2, 4, 2]
output: def remove_item(lst, item):
      return [x for x in lst if x != item]