Remove unnecessary serde_derive dependency declaration

We already express the same thing through the serde `derive` feature.

Cargo.lock

@@ -3498,7 +3498,6 @@ dependencies = [
  "rust_decimal",
  "serde",
  "serde_cbor",
- "serde_derive",
  "serde_json",
  "sha2 0.9.2",
  "sigma_fun",

swap/Cargo.toml

@@ -43,7 +43,6 @@ reqwest = { version = "0.11", default-features = false }
 rust_decimal = "1.10"
 serde = { version = "1", features = ["derive"] }
 serde_cbor = "0.11"
-serde_derive = "1.0"
 serde_json = "1"
 sha2 = "0.9"
 sigma_fun = { git = "https://github.com/LLFourn/secp256kfun", features = ["ed25519", "serde"] }