[eprh] Prepare for 7.0.0

For 7.0.0:

Slim down presets to just 3 configurations:

- `recommended-legacy`: legacy config with all recommended rules
- `recommended`: flat config with all recommended rules, and
- `recommended-experimental`: flat config with all recommended rules plus new bleeding edge experimental compiler rules

Removed:
- `recommended-latest-legacy`
- `flat/recommended configs`