Clean up doc, private func, removed unused file

Various clean-ups as I walked through the code:
- Removed now-unused tests/api/utils.py
- Improve description of various API objects
- Make entity_update() a private function like the other _entity_*()
- Streamline # BEGIN lines in db/api.py
- Add missing final periods in some docstrings

Change-Id: I1c720810bb29b86f5d446e912ced80a24a70c9af
Merge "Clean up doc, private func, removed unused file"