`debcargo build-order` breaks in certain cases involving deleted features.

The following discussion from !50 (merged) should be addressed:

• @infinity0 started a discussion: (+8 comments)

Test code:

#[test]
fn test_feature_resolution() -> () {
    let fd_find_version = "8.7.0";
    let seed_dep = crate_name_ver_to_dep("fd-find", Some(fd_find_version)).unwrap();
    let res = CrateInfo::new_from_dependency(&seed_dep, false).unwrap();
    let clap_dep = res
        .dependencies()
        .iter()
        .find(|dep| dep.package_name() == "clap")
        .unwrap();

    eprintln!(
        "fd-find {} depends on clap {} with features {:?}",
        fd_find_version,
        clap_dep.version_req(),
        clap_dep.features(),
    );

    let _res = CrateInfo::new_from_dependency(&clap_dep, false).unwrap(); // fails
}