sled-agent-client doesn't depend on sled-storage (#4829)

If someone is incrementally working on sled-storage, poking at something
fully unrelated to the API, they’ll need to rebuild all of Nexus. Why?

We have the following dependencies:
- Nexus depends on sled_agent_client
- sled_agent_client depends on sled_storage
… so if you poke at sled_storage, you gotta rebuild Nexus.

This PR removes that (not actually needed) dependency -- now, updates to
sled-storage do not cause Nexus to rebuild

clients/sled-agent-client/Cargo.toml

@@ -15,6 +15,5 @@ reqwest = { workspace = true, features = [ "json", "rustls-tls", "stream" ] }
 schemars.workspace = true
 serde.workspace = true
 slog.workspace = true
-sled-storage.workspace = true
 uuid.workspace = true
 omicron-workspace-hack.workspace = true