input: Write a function to delete a certain node from a linked list.
  
  class Node:
      def __init__(self, data):
          self.data = data
          self.next = None
  
  class LinkedList:
      def __init__(self):
          self.head = None
  
      def deleteNode(self, node):
          if (node is None or self.head is None):
              return
          if self.head == node:
              self.head = node.next
              node = None
              return
          current = self.head
          while current.next is not None and current.next != node:
              current = current.next
          if current.next is None:
              return
          current.next = node.next
          node = None
          
  llist = LinkedList()
  llist.head = Node(1)
  second = Node(2)
  third = Node(3)
  fourth = Node(4)
  llist.head.next = second
  second.next = third
  third.next = fourth
  llist.deleteNode(third)
  assert llist.head.next.next.data == 4
  assert llist.deleteNode(None) is None
  assert llist.deleteNode(llist.head.next.next) is None
output: def deleteNode(self, node):
      if (node is None or self.head is None):
          return
      if self.head == node:
          self.head = node.next
          node = None
          return
      current = self.head
      while current.next is not None and current.next != node:
          current = current.next
      if current.next is None:
          return
      current.next = node.next
      node = None