Remove more obsolete Devise code

The initializer was a no-op override after our Devise upgrade

config/initializers/devise_rails8_patch.rb

@@ -1,11 +0,0 @@
-# See https://alvincrespo.hashnode.dev/rails-8s-lazy-route-loading-devise
-# TODO remove when Devise is fixed
-require 'devise'
-Devise # make sure it's already loaded
-
-module Devise
-  def self.mappings
-    Rails.application.try(:reload_routes_unless_loaded)
-    @@mappings
-  end
-end