Remove dead code in Admin::ProductsController

This is related to some of the data-loading for index actions inherited from Spree's Admin::ResourceController, but we don't actually use it any more...

app/controllers/spree/admin/products_controller.rb

@@ -127,26 +127,7 @@ module Spree
       end
 
       def collection
-        return @collection if @collection.present?
-
-        params[:q] ||= {}
-        params[:q][:deleted_at_null] ||= "1"
-
-        params[:q][:s] ||= "name asc"
-        @collection = Spree::Product
-        @collection = @collection.with_deleted if params[:q].delete(:deleted_at_null).blank?
-        # @search needs to be defined as this is passed to search_form_for
-        @search = @collection.ransack(params[:q])
-        @collection = @search.result.
-          managed_by(spree_current_user).
-          group_by_products_id.
-          includes(product_includes)
-
-        if params[:q][:s].include?("master_default_price_amount")
-          # PostgreSQL compatibility
-          @collection = @collection.group("spree_prices.amount")
-        end
-        @collection
+        nil
       end
 
       def product_includes