Fix stray bugs on minor codepaths

I ran `rails zeitwerk:check`, which eager-loads the app, and it found two problems: `closet_group.rb` doesn't define `ClosetGroup` (cuz it's empty), and I left in a reference to a cache sweeper observer oops. Goodbye!

app/controllers/pets_controller.rb

@@ -5,8 +5,6 @@ class PetsController < ApplicationController
 
   protect_from_forgery except: :submit
   before_action :local_only, only: :submit
-  
-  cache_sweeper :user_sweeper
 
   def load
     if params[:name] == '!'