Update deprecation message.

Author: damrobi

mithril-stm/src/bls_multi_signature/verification_key.rs

@@ -164,7 +164,10 @@ impl BlsVerificationKeyProofOfPossession {
     /// manually.
     // If we are really looking for performance improvements, we can combine the
     // two final exponentiations (for verifying k1 and k2) into a single one.
-    #[deprecated(since = "0.5.0", note = "Use `verify_proof_of_possession` instead")]
+    #[deprecated(
+        since = "0.5.0",
+        note = "The verification of the proof of possession is not part of the public API any more"
+    )]
     pub fn check(&self) -> Result<(), MultiSignatureError> {
         Self::verify_proof_of_possession(self)
     }