input: Write a python function to remove a specified number from a list.
  assert remove_num([1, 2, 3, 4, 2, 5], 2) == [1, 3, 4, 5]
  assert remove_num([10, 20, 30, 40, 50], 30) == [10, 20, 40, 50]
  assert remove_num([5, 5, 5, 5], 5) == []
  assert remove_num([7, 8, 9, 10], 11) == [7, 8, 9, 10]
output: def remove_num(lst, num):
      return [x for x in lst if x != num]