Dead code warnings in nightly and beta

Building with nightly produces a lot of warnings. This isn't great and it will become a significant problem when this version of Rust becomes stable.

See also #1383 (closed) which is slightly different.

-*- mode: compilation; default-directory: "~/Rustup/Arti/arti/" -*-
Compilation started at Mon Jun 17 18:50:35

nailing-cargo +nightly check --all-features --workspace --all-targets
nailing-cargo: out-of-tree, git, building in: `/home/ian/Rustup/Arti/Build/arti'
nailing-cargo: using really to run as user `rustcargo'
nailing-cargo: *WARNING* cwd is not in Cargo.nail thbough it has Cargo.toml!
nailing-cargo: nailed (0 manifests, 0 packages)
nailing-cargo: invoking: cargo +nightly check --locked --offline --all-features --workspace --all-targets
warning: struct `CreateFastServer` is never constructed
  --> crates/tor-proto/src/crypto/handshake/fast.rs:74:19
   |
74 | pub(crate) struct CreateFastServer;
   |                   ^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: struct `NtorServer` is never constructed
  --> crates/tor-proto/src/crypto/handshake/ntor.rs:43:19
   |
43 | pub(crate) struct NtorServer;
   |                   ^^^^^^^^^^

warning: fields `pk` and `sk` are never read
  --> crates/tor-proto/src/crypto/handshake/ntor.rs:78:5
   |
76 | pub(crate) struct NtorSecretKey {
   |                   ------------- fields in this struct
77 |     /// Public key components; must match those held by the client.
78 |     pk: NtorPublicKey,
   |     ^^
...
81 |     sk: StaticSecret,
   |     ^^

warning: method `matches_pk` is never used
  --> crates/tor-proto/src/crypto/handshake/ntor.rs:97:8
   |
85 | impl NtorSecretKey {
   | ------------------ method in this implementation
...
97 |     fn matches_pk(&self, pk: &PublicKey) -> Choice {
   |        ^^^^^^^^^^

warning: function `server_handshake_ntor_v1` is never used
   --> crates/tor-proto/src/crypto/handshake/ntor.rs:267:4
    |
267 | fn server_handshake_ntor_v1<R, T>(
    |    ^^^^^^^^^^^^^^^^^^^^^^^^

warning: function `server_handshake_ntor_v1_no_keygen` is never used
   --> crates/tor-proto/src/crypto/handshake/ntor.rs:287:4
    |
287 | fn server_handshake_ntor_v1_no_keygen<T>(
    |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: `tor-proto` (lib) generated 6 warnings
warning: constant `REMOVE_CONSENSUS` is never used
   --> crates/tor-dirmgr/src/storage/sqlite.rs:865:7
    |
865 | const REMOVE_CONSENSUS: &str = "
    |       ^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: constant `DELETE_BRIDGEDESC` is never used
   --> crates/tor-dirmgr/src/storage/sqlite.rs:947:7
    |
947 | const DELETE_BRIDGEDESC: &str = "DELETE FROM BridgeDescs WHERE bridge_line = ?;";
    |       ^^^^^^^^^^^^^^^^^

warning: `tor-dirmgr` (lib) generated 2 warnings
warning: associated constant `BUCKET_CAPACITY` is never used
  --> crates/equix/src/bucket_array/hash.rs:24:11
   |
19 | pub(crate) trait Shape<K: Key> {
   |                  ----- associated constant in this trait
...
24 |     const BUCKET_CAPACITY: usize;
   |           ^^^^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: `equix` (lib) generated 1 warning
warning: constant `DELETE_BRIDGEDESC` is never used
   --> crates/tor-dirmgr/src/storage/sqlite.rs:947:7
    |
947 | const DELETE_BRIDGEDESC: &str = "DELETE FROM BridgeDescs WHERE bridge_line = ?;";
    |       ^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: `tor-dirmgr` (lib test) generated 1 warning
warning: `equix` (lib test) generated 1 warning (1 duplicate)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.07s
nailing-cargo: unnailed.  status 0.

Compilation finished at Mon Jun 17 18:50:37