Clean up Notes

- convert to block comments
- move Note [Injectivity check ...] from FamInst to FamInstEnv
Revert "Clean up Notes"

This reverts commit eb937f47705b85579f76b8b05342af1541b384db.
Move Note [Injectivity ...] from FamInst to FamInstEnv
Clean up rnFamDecl according to RAE's suggestions