removed 1st edition code

17-it-generator/tree/step2/tree.py

@@ -1,14 +0,0 @@
-def tree(cls):
-    yield cls.__name__, 0
-    yield from sub_tree(cls)              # <1>
-
-
-def sub_tree(cls):
-    for sub_cls in cls.__subclasses__():
-        yield sub_cls.__name__, 1         # <2>
-
-
-if __name__ == '__main__':
-    for cls_name, level in tree(BaseException):
-        indent = ' ' * 4 * level
-        print(f'{indent}{cls_name}')