Fixes a mistake made in the previous change to tools/init.py.

In particular, the comment describing how to run the build_graph and pack_nbrs
tools should not include ".py" in the module names.

PiperOrigin-RevId: 274680087

neural_structured_learning/tools/__init__.py

@@ -4,8 +4,8 @@
 from the command-line as follows:
 
 ```sh
-$ python -m neural_structured_learning.tools.build_graph.py ...
-$ python -m neural_structured_learning.tools.pack_nbrs.py ...
+$ python -m neural_structured_learning.tools.build_graph ...
+$ python -m neural_structured_learning.tools.pack_nbrs ...
 ```
 
 For details on the command-line usage for these programs, see the