API cleanup notes

Dumping notes here as I work on #1197

* longControl.pid -> longControl.accel?
* remove all the "openpilot", "controlsd", etc.
* carParams.safetyModel should use the int values, needed for interacting with panda https://github.com/commaai/opendbc/blob/cbad7f00669904646e74e8f1b8f66e5ead62b6b9/opendbc/car/panda_runner.py#L26
* abstract out fault handling and more into "ready to control"
* abstract away "pcmCruise"
* move "VCruiseHelper" and relevant state: https://github.com/commaai/openpilot/blob/f59a1bf00344432acad686f4813069e7c0c063b6/selfdrive/controls/lib/drive_helpers.py#L42

Start by reviewing issue #1197, which this note says is the active work context. Then inspect the referenced locations in opendbc/car/panda_runner.py and openpilot's selfdrive/controls/lib/drive_helpers.py, along with each listed cleanup item. The work is done only when the scope and implementation of all listed API and control abstractions are resolved.

Written by the indexing model from the issue text.