Remove old protocol ChallengeResponse code.

acme/acme/challenges.py

@@ -39,15 +39,6 @@ class ChallengeResponse(interfaces.ClientRequestableResource,
     TYPES = {}
     resource_type = 'challenge'
 
-    @classmethod
-    def from_json(cls, jobj):
-        if jobj is None:
-            # if the client chooses not to respond to a given
-            # challenge, then the corresponding entry in the response
-            # array is set to None (null)
-            return None
-        return super(ChallengeResponse, cls).from_json(jobj)
-
 
 @Challenge.register
 class SimpleHTTP(DVChallenge):

acme/acme/challenges_test.py

@@ -16,13 +16,6 @@ CERT = test_util.load_cert('cert.pem')
 KEY = test_util.load_rsa_private_key('rsa512_key.pem')
 
 
-class ChallengeResponseTest(unittest.TestCase):
-
-    def test_from_json_none(self):
-        from acme.challenges import ChallengeResponse
-        self.assertTrue(ChallengeResponse.from_json(None) is None)
-
-
 class SimpleHTTPTest(unittest.TestCase):
 
     def setUp(self):