Remove higher rank polymorphism extensions for now
This branch removes support for the
RankNTypes language extension and its changes to the AST (e.g. by reintroducing
The idea here is to defer support for higher-rank polymorphism due to longer-standing issues in the frontend (see curry-frontend#77) and focus on having a stable main version of the frontend again.
A future merge request could re-revert these changes to include higher-rank-polymorphism support again.