[WORKER] Remove unused stats_client.py file

This code was originally used to start a new thread that polled
the worker for statistics. This is gathered via the STATS message
now, so this is unused code.

Change-Id: I1cc7a1af1717f910308ac83967c21df1f705d8f8
[API] Fix logging line

Old style logging was causing an exception, and IP deletes to fail.

Change-Id: Ifc3b7cfed6c6140d3327d863840c79c03df8ffbd