Fixes #4734 -- Deal with deprecated things (#4736)

* Fixes #4734 -- Deal with deprecated things

- Make year based aliases of PersistentlyDeprecated so we can easily assess age
- Removed encode/decode rfc6979 signature
- Removed Certificate.serial

* Unused import

2 files changed, 1 insertions, 11 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/utils.py b/src/cryptography/hazmat/backends/openssl/utils.py
index 363f3d2c..ee472c0e 100644
--- a/src/cryptography/hazmat/backends/openssl/utils.py
+++ b/src/cryptography/hazmat/backends/openssl/utils.py
@@ -64,6 +64,6 @@ def _warn_sign_verify_deprecated():
     warnings.warn(
         "signer and verifier have been deprecated. Please use sign "
         "and verify instead.",
-        utils.PersistentlyDeprecated,
+        utils.PersistentlyDeprecated2017,
         stacklevel=3
     )
diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index ac1838c6..b3eb797d 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -6,7 +6,6 @@ from __future__ import absolute_import, division, print_function
 
 import datetime
 import operator
-import warnings
 
 from cryptography import utils, x509
 from cryptography.exceptions import UnsupportedAlgorithm
@@ -63,15 +62,6 @@ class _Certificate(object):
             )
 
     @property
-    def serial(self):
-        warnings.warn(
-            "Certificate serial is deprecated, use serial_number instead.",
-            utils.PersistentlyDeprecated,
-            stacklevel=2
-        )
-        return self.serial_number
-
-    @property
     def serial_number(self):
         asn1_int = self._backend._lib.X509_get_serialNumber(self._x509)
         self._backend.openssl_assert(asn1_int != self._backend._ffi.NULL)