fix(avow-protocol): remove avow-lib and .machine_readable from thin binding

The thin binding should only contain BINDING.adoc pointing to the canonical
repo. The avow-lib/ directory and .machine_readable/ were inadvertently
restored during merge conflict resolution but belong in the canonical
avow-protocol repository per the thin-binding design.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Author: hyperpolymath