Fix activity being rendered within activity due to caching (#11271)

Fix #11270

app/serializers/activitypub/collection_serializer.rb

@@ -7,8 +7,6 @@ class ActivityPub::CollectionSerializer < ActivityPub::Serializer
     super
   end
 
-  cache key: 'collection', expires_in: 3.minutes
-
   attribute :id, if: -> { object.id.present? }
   attribute :type
   attribute :total_items, if: -> { object.size.present? }