input: Write a function to delete a certain element from a linked list. The function should take a linked list object and the node to be deleted as input and modify the linked list by removing the specified node.
  assert delete_node(llist, 3) == [2, 4, 5]
  assert delete_node(llist, 5) == [2, 3, 4]
  assert delete_node(llist, 2) == [3, 4, 5]
  assert delete_node(llist, 1) == [2, 3, 4, 5]
  assert delete_node(llist, 6) == [2, 3, 4, 5]
output: def delete_node(llist, node):
      if llist.val == node:
          return llist.next
      current = llist
      while current.next:
          if current.next.val == node:
              current.next = current.next.next
              return llist
          current = current.next
      return llist