[REPO] Remove duplicate and misplaced files from root

[ezehf2]

Several files are sitting loose at the root of the repository that need to be cleaned up. The files subscriber.py, subscriber.py (typo), publisher.py, and mqtt_test.py are all sitting at the root level and are either duplicates or early test files. The correct subscriber lives in mqtt/subscriber.py. Delete the root-level duplicates, move publisher.py and mqtt_test.py into the mqtt/ folder if they are still needed, or delete them if they are old experiments. Commit with message [REPO] Clean up duplicate and misplaced root files.