Don't derive Serialize & Deserialize for txids

Deriving `serde::Serialize` & `serde::Deserialize` for
`transaction::Hash` was superfluous, and we didn't need it anywhere in
the code.

zebra-chain/src/transaction/hash.rs

@@ -34,7 +34,6 @@ use std::{fmt, sync::Arc};
 use proptest_derive::Arbitrary;
 
 use hex::{FromHex, ToHex};
-use serde::{Deserialize, Serialize};
 
 use crate::serialization::{
     ReadZcashExt, SerializationError, WriteZcashExt, ZcashDeserialize, ZcashSerialize,
@@ -56,7 +55,7 @@ use super::{txid::TxIdBuilder, AuthDigest, Transaction};
 ///
 /// [ZIP-244]: https://zips.z.cash/zip-0244
 /// [Spec: Transaction Identifiers]: https://zips.z.cash/protocol/protocol.pdf#txnidentifiers
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize, Hash)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 #[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
 pub struct Hash(pub [u8; 32]);