Update doubly_linked_list_two.py

Author: MaximSmolskiy

Diff for: data_structures/linked_list/doubly_linked_list_two.py

@@ -84,7 +84,6 @@ def set_tail(self, node: Node) -> None:
         if self.head is None:
             self.set_head(node)
         else:
-            assert self.tail
             self.insert_after_node(self.tail, node)
 
     def insert(self, value: int) -> None: