Fixes signing Create activities

and some tests for the base_model

bookwyrm/models/base_model.py

@@ -96,7 +96,7 @@ class ActivitypubMixin:
         ''' returns the object wrapped in a Create activity '''
         activity_object = self.to_activity()
 
-        signer = pkcs1_15.new(RSA.import_key(user.private_key))
+        signer = pkcs1_15.new(RSA.import_key(user.key_pair.private_key))
         content = activity_object['content']
         signed_message = signer.sign(SHA256.new(content.encode('utf8')))
         create_id = self.remote_id + '/activity'

bookwyrm/models/status.py

@@ -44,11 +44,6 @@ class Status(OrderedCollectionPageMixin, BookWyrmModel):
     )
     objects = InheritanceManager()
 
-    @property
-    def ap_replies(self):
-        ''' structured replies block '''
-        return self.to_replies()
-
     activity_serializer = activitypub.Note
     serialize_reverse_fields = ['attachments']