test_rust.sh fails on src/rust/crypto

The latest travis builds fail on the rust tests after legacy/trac#26258 (moved) got merged (i guess). Here are some fails:

  --> external/crypto_digest.rs:74:1
   |
74 | const N_DIGEST_ALGORITHMS: usize = DIGEST_SHA3_512 as usize + 1;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(dead_code)] on by default

warning: type alias is never used: `smartlist_t`
   --> external/crypto_digest.rs:120:1
    |
120 | type smartlist_t = Stringlist;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: constant item is never used: `N_DIGEST_ALGORITHMS`
  --> external/crypto_digest.rs:74:1
   |
74 | const N_DIGEST_ALGORITHMS: usize = DIGEST_SHA3_512 as usize + 1;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(dead_code)] on by default

warning: type alias is never used: `smartlist_t`
   --> external/crypto_digest.rs:120:1
    |
120 | type smartlist_t = Stringlist;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    Finished dev [unoptimized + debuginfo] target(s) in 3.39 secs
     Running /home/travis/build/torproject/tor/tor-0.3.4.2-alpha-dev/_build/src/rust/target/debug/deps/external-99409f0e61b6d8c2

See https://api.travis-ci.org/v3/job/392350333/log.txt etc.