In binary_search_tree.py, unnecessary BinarySearchTree class causes confusion

[EricW87]

In binary_search_tree.py, below the BSTNode class definition, there is extra code that uses the BinarySearchTree class. This class is undefined. It is not referenced in the instructions, and causes difficult to decipher errors when you first start on the project.

Possible solutions:

1. Change BinarySearchTree to BSTNode
2. Add a BinarySearchTree class derived from BSTNode
3. Add instructions to tell the student to write AJ Genung WIP #2.