[Michocoq] ignore annotations on sum types everywhere but in parameter

This is a fix for #49 (closed). The problem was that Mi-Cho-Coq type system expects all types to exactly match but Michelson only requires types to match upto annotations. The only place where annotations appear in Mi-Cho-Coq's internal representation is on the or types because they are used for entrypoints.

This fix strips annotations during parsing everywhere but in the paramter type.