Remove unused declarations / check obj. LIGO

This MR prevents corner case failure when compiling a contract that contains Test primitives or types.

It does mainly two things:

1. It will remove unused Declaration_constants / Declaration_modules, so that if someone was using a Test primitive in an unused declaration, compile-contract will still successfully work.

2. The pass checking that Test primitives/types are not used is moved from the interpreter to self_ast_typed, and it is applied after removing unused declarations.

• has a changelog entry