Merge branch 'rs-note-model-cleanup' into 'master'

Minor Note model cleanup

Remove `Note#noteable_type_name`

This method was added in Dec 2012, its single use was removed two days
later, and it's been there ever since.

---

Remove `Note#system?` "override"

This method was duplicating default Rails behavior.

See merge request !3104

Former-commit-id: 20ed08ed

app/models/note.rb

@@ -323,10 +323,6 @@ class Note < ActiveRecord::Base
     noteable
   end
-  def noteable_type_name
-    noteable_type.downcase if noteable_type.present?
-  end
-
   # FIXME: Hack for polymorphic associations with STI
   #        For more information visit http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#label-Polymorphic+Associations
   def noteable_type=(noteable_type)
@@ -346,10 +342,6 @@ class Note < ActiveRecord::Base
     Event.reset_event_cache_for(self)
   end
-  def system?
-    read_attribute(:system)
-  end
-
   def downvote?
     is_award && note == "thumbsdown"
   end