avoid unnecessary double-hex-conversion

zeroize has to be kept at 1.3.0 for now to keep compatibility with
another dependency of the Pod, chacha20poly1305.

Remove the unnecessary uuid dependency along the way

```
thread 'main' panicked at 'there is no reactor running, must be called from the context of Tokio runtime', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.2.22/src/io/driver/mod.rs:201:9
```

This commit also fixes a cargo-audit warning

By default, warp includes multipart and websockets support.

We don't need either yet, so we might be better off
by not asking them in the first place (including time to compile).