Remove: ModuleProgram struct

[LesterEvSe]

Resolves issue #321

[KyrylR]

We should mention this change in a CHANGELOG.md

[KyrylR]

Found a few leftovers:

• just check_fuzz still calls deleted target parse_witness_module_rtt: justfile#L41
• parse_witness_json_rtt test still uses removed WitnessValues::parse_from_str: parse_witness_json_rtt.rs#L23-L32
• AST-side module analysis scaffolding looks unused now: ast.rs#L407-L455, ast.rs#L1571-L1609

cargo test --manifest-path fuzz/Cargo.toml --bin parse_witness_json_rtt fails with E0599 because of the second one

[LesterEvSe]

* AST-side module analysis scaffolding looks unused now: [`ast.rs#L407-L455`](https://github.com/BlockstreamResearch/SimplicityHL/blob/7ded9ef447acacdacfc560eed6e8e042e6cc1c7e/src/ast.rs#L407-L455), [`ast.rs#L1571-L1609`](https://github.com/BlockstreamResearch/SimplicityHL/blob/7ded9ef447acacdacfc560eed6e8e042e6cc1c7e/src/ast.rs#L1571-L1609)

Yes, that's right. But the fundamentals of this can be used when solving this issue: #318