Perform single key hash in key registry read

[nventuro]

The new key registry introduced in #7523 hashes keys twice, once for the hinted registry keys, and once for the hinted canonical keys. This results in an extra ~400 gates per set of keys read.

We can simplify this to a single hash if the unconstrained hint always returns the correct hint (either the registry or canonical set depending on the registry value) and so remove these extra gates:

let hinted_keys = get_keys_hint(); // unconstrained
let hinted_keys_hash = hinted_keys.hash();

let registry_key_hash = historical_read();
if registry_key_hash != 0 {
 assert_eq(registry_key_hash, hinted_keys_hash);
} else {
 let partial_address = get_partial_address() // unconstrained
 assert_eq(account, Address::compute(hinted_keys_hash, partial_address));
}

hinted_keys

[nventuro]

We're dropping key rotation as of #8613, so we only ever hash the address preimage once, meaning we don't need this.