Agreement docs: Eliminate redundant nested peer_public_key in example.

src/agreement.rs

@@ -35,11 +35,10 @@
 //! let peer_public_key = {
 //!     // In a real application, the peer public key would be parsed out of a
 //!     // protocol message. Here we just generate one.
-//!     let peer_public_key = {
-//!         let peer_private_key =
-//!             agreement::EphemeralPrivateKey::generate(&agreement::X25519, &rng)?;
-//!         peer_private_key.compute_public_key()?
-//!     };
+//!     let peer_private_key =
+//!         agreement::EphemeralPrivateKey::generate(&agreement::X25519, &rng)?;
+//!     peer_private_key.compute_public_key()?
+//! };
 //!
 //!     agreement::UnparsedPublicKey::new(&agreement::X25519, peer_public_key)
 //! };