Remove duplicate read::hash() and read::hash_by_height() consensus-critical code

[teor2345]

Motivation

Zebra has two duplicate state functions for reading a block hash: read::hash() and read::hash_by_height(). We don't want to have duplicate code in Zebra, because it risks breaking consensus. It's also hard to maintain and audit.

This is a simple search-and-replace fix.

zebra/zebra-state/src/service/read/find.rs

Lines 111 to 112 in 53e836e

	/// Return the hash for the block at `height`, if `height` is in `chain` or `db`.
	pub fn hash_by_height<C>(chain: Option<C>, db: &ZebraDb, height: Height) -> Option<block::Hash>

zebra/zebra-state/src/service/read/block.rs

Lines 187 to 190 in 53e836e

	#[cfg(feature = "getblocktemplate-rpcs")]
	/// Returns the [`Hash`] given [`block::Height`](zebra_chain::block::Height), if it exists in
	/// the non-finalized `chain` or finalized `db`.
	pub fn hash<C>(chain: Option<C>, db: &ZebraDb, height: Height) -> Option<zebra_chain::block::Hash>

Testing

This change will improve testing, because the existing tests will all check the same function, rather than some tests checking one function, and some checking the other function.

Related Work

Discovered as part of PR #5894.

[teor2345]

@mpguerra can we schedule this fix soon?

It's very small, and it's a consensus compatibility risk.

[mpguerra]

@teor2345 can you please add an estimate to this issue?