Remove unused module from lib

I was looking for library files that may be used but are not loaded.
I would then add the missing `require` statements. But I found that this
module isn't used any more.

Usage removed in:
310d1b3726

.rubocop_todo.yml

@@ -1037,7 +1037,6 @@ Style/FrozenStringLiteralComment:
     - 'lib/open_food_network/i18n_config.rb'
     - 'lib/open_food_network/lettuce_share_report.rb'
     - 'lib/open_food_network/locking.rb'
-    - 'lib/open_food_network/model_class_from_controller_name.rb'
     - 'lib/open_food_network/order_and_distributor_report.rb'
     - 'lib/open_food_network/order_cycle_form_applicator.rb'
     - 'lib/open_food_network/order_cycle_management_report.rb'

lib/open_food_network/model_class_from_controller_name.rb

@@ -1,8 +0,0 @@
-module OpenFoodNetwork
-  module ModelClassFromControllerName
-    # Equivalent to CanCan's "authorize_resource :class => false" (see https://github.com/ryanb/cancan/blob/master/lib/cancan/controller_resource.rb#L146)
-    def model_class
-      self.class.to_s.sub("Controller", "").underscore.split('/').last.singularize.to_sym
-    end
-  end
-end