remove bare Serialize and Deserialize progenitor patch imperatives

[ahl]

This doesn't update progenitor as it would require oxidecomputer/omicron#6258 as well, but I've tested both together locally with an updated progenitor.

[gjcolombo]

LGTM--thanks for taking the time to do this.

[gjcolombo]

nit: can also remove Clone and Debug from this one

[ahl]

Thanks

[davepacheco]

Recording here for future searchability: this fixes a problem I ran into when trying to deal with oxidecomputer/testbed#62. While trying to pull a fix for oxidecomputer/falcon#81 into my testbed clone, updating libfalcon also wound up updating propolis-client and progenitor and typify. But the new Progenitor (post oxidecomputer/progenitor#882) doesn't use serde::{Deserialize, Serialize} and so it doesn't work with propolis-client prior to this PR. In particular, my testbed build failed with:

error: cannot find derive macro `Deserialize` in this scope
  --> /home/dap/.cargo/git/checkouts/propolis-12517f89d3d9f483/722bedc/lib/propolis-client/src/lib.rs:8:1
   |
8  | / progenitor::generate_api!(
9  | |     spec = "../../openapi/propolis-server.json",
10 | |     interface = Builder,
11 | |     tags = Separate,
...  |
31 | |     }
32 | | );
   | |_^
   |
   = help: consider importing this derive macro:
           serde::Deserialize
   = note: this error originates in the macro `progenitor::generate_api` (in Nightly builds, run with -Z macro-backtrace for more info)

This PR should fix that, though in testbed#62 I also avoided pulling in the new progenitor because it wasn't what I was trying to do.