zcash_note_encryption: Remove `esk` check requirement from `Domain::parse_note_plaintext_without_memo_ovk`

This method is only called from `try_output_recovery_with_ock`, and we
can instead rely on the check performed in `check_note_validity`,
reducing the number of checks that `Domain` implementations need to
perform.

The `esk` and `ephemeral_key` parameters become unused, and will be
removed in a subsequent commit (as this change needs to be synchronized
with the `orchard` crate).


Extracted from: a115a8f00f

src/lib.rs

@@ -229,8 +229,6 @@ pub trait Domain {
     ///   which may be passed via `self`).
     /// - The note plaintext contains valid encodings of its various fields.
     /// - Any domain-specific requirements are satisfied.
-    /// - `ephemeral_key` can be derived from `esk` and the diversifier within the note
-    ///   plaintext.
     ///
     /// `&self` is passed here to enable the implementation to enforce contextual checks,
     /// such as rules like [ZIP 212] that become active at a specific block height.