Refactor Product and Promotion ransackable_scopes

By using allowed_ransackable_scopes which was introduced in the last
commit, stores will be able to easily concatenate to the arrays already
declared on Product and Promotion in Solidus.

core/app/models/spree/product.rb

@@ -133,10 +133,7 @@ def find_or_build_master
 
     self.allowed_ransackable_associations = %w[stores variants_including_master master variants]
     self.allowed_ransackable_attributes = %w[name slug]
-
-    def self.ransackable_scopes(_auth_object = nil)
-      %i(available with_discarded with_variant_sku_cont with_all_variant_sku_cont with_kept_variant_sku_cont)
-    end
+    self.allowed_ransackable_scopes = %i[available with_discarded with_variant_sku_cont with_all_variant_sku_cont with_kept_variant_sku_cont]
 
     # @return [Boolean] true if there are any variants
     def has_variants?

core/app/models/spree/promotion.rb

@@ -54,9 +54,7 @@ class Promotion < Spree::Base
 
     self.allowed_ransackable_associations = ['codes']
     self.allowed_ransackable_attributes = %w[name path promotion_category_id]
-    def self.ransackable_scopes(*)
-      %i(active)
-    end
+    self.allowed_ransackable_scopes = %i[active]
 
     def self.order_activatable?(order)
       order && !UNACTIVATABLE_ORDER_STATES.include?(order.state)