input: Write a function to remove all the duplicates from a linked list in Python.
  
  ### Input:
  list_nodes = [7, 14, 28, 28, 28, 35, 49]
  
  ### Output:
  class Node: 
      # Function to initialise the node object 
      def __init__(self, data): 
          self.data = data # Assign data 
          self.next = None # Initialize next as null 
    
    
  # Linked List class contains a Node object 
  class LinkedList: 
      # Function to initialize head 
      def __init__(self): 
          self.head = None
  
      def remove_duplicates(self):
          curr_node = self.head 
          unique_nodes = set()
          previous_node = None
          while curr_node != None: 
              if curr_node.data in unique_nodes: 
                  previous_node.next = curr_node.next
              else:
                  unique_nodes.add(curr_node.data) 
                  previous_node = curr_node
              curr_node = curr_node.next
  
      def insert_node(self, data): 
      # Create a new node 
          new_node = Node(data) 
          # Check if list is empty
          if self.head is None: 
              self.head = new_node 
              return
          # Otherwise, traverse to the end of list before 
          # inserting the new Node 
          last = self.head 
          while (last.next): 
              last = last.next
          last.next =  new_node
  
  # Test cases
  llist = LinkedList()
  llist.insert_node(7)
  llist.insert_node(14)
  llist.insert_node(28)
  llist.insert_node(28)
  llist.insert_node(28)
  llist.insert_node(35)
  llist.insert_node(49)
  llist.remove_duplicates()
  assert llist.head.data == 7
  assert llist.head.next.data == 14
  assert llist.head.next.next.data == 28
  assert llist.head.next.next.next.data == 35
  assert llist.head.next.next.next.next.data == 49
  assert llist.head.next.next.next.next.next == None
output: 
  def remove_duplicates(self):
      curr_node = self.head 
      unique_nodes = set()
      previous_node = None
      while curr_node != None: 
          if curr_node.data in unique_nodes: 
              previous_node.next = curr_node.next
          else:
              unique_nodes.add(curr_node.data) 
              previous_node = curr_node
          curr_node = curr_node.next
  