Cleanup #attributes method

Since we're prepending the ActiveRecord::Extension module, we
can take advantage of it and avoid using an alias to extend the
original #attributes method.

lib/gitlab/markdown_cache/active_record/extension.rb

@@ -7,31 +7,25 @@ module Gitlab
         extend ActiveSupport::Concern
 
         included do
+          # Using before_update here conflicts with elasticsearch-model somehow
+          before_create :refresh_markdown_cache, if: :invalidated_markdown_cache?
+          before_update :refresh_markdown_cache, if: :invalidated_markdown_cache?
+        end
+
         # Always exclude _html fields from attributes (including serialization).
         # They contain unredacted HTML, which would be a security issue
-          alias_method :attributes_before_markdown_cache, :attributes
         def attributes
-            attrs = attributes_before_markdown_cache
+          attrs = super
           html_fields = cached_markdown_fields.html_fields
           whitelisted = cached_markdown_fields.html_fields_whitelisted
           exclude_fields = html_fields - whitelisted
 
-            exclude_fields.each do |field|
-              attrs.delete(field)
-            end
-
-            if whitelisted.empty?
-              attrs.delete('cached_markdown_version')
-            end
+          attrs.except!(*exclude_fields)
+          attrs.delete('cached_markdown_version') if whitelisted.empty?
 
           attrs
         end
 
-          # Using before_update here conflicts with elasticsearch-model somehow
-          before_create :refresh_markdown_cache, if: :invalidated_markdown_cache?
-          before_update :refresh_markdown_cache, if: :invalidated_markdown_cache?
-        end
-
         def changed_markdown_fields
           changed_attributes.keys.map(&:to_s) & cached_markdown_fields.markdown_fields.map(&:to_s)
         end