remind people we're going to remove verifier/signer (#6640)

Author: reaperhulk

CHANGELOG.rst

@@ -9,6 +9,11 @@ Changelog
  .. note:: This version is not yet released and is under active development.
 
 
+* **FINAL DEPRECATION** Support for ``verifier`` and ``signer`` on our
+  asymmetric key classes was deprecated in version 2.1. These functions had an
+  extended deprecation due to usage, however the next version of
+  ``cryptography`` will drop support. Users should migrate to ``sign`` and
+  ``verify``.
 * The entire :doc:`/x509/index` layer is now written in Rust. This allows
   alternate asymmetric key implementations that can support cloud key
   management services or hardware security modules provided they implement

src/cryptography/hazmat/backends/openssl/utils.py

@@ -59,8 +59,9 @@ def _check_not_prehashed(signature_algorithm):
 
 def _warn_sign_verify_deprecated():
     warnings.warn(
-        "signer and verifier have been deprecated. Please use sign "
-        "and verify instead.",
+        "signer and verifier have been deprecated since 2.1. Please use sign "
+        "and verify instead. Support for these functions will be dropped"
+        " in the next release of cryptography (37.0).",
         utils.PersistentlyDeprecated2017,
         stacklevel=3,
     )