Remove Spree::*.calculators method

Class method `calculators` on Spree::CalculatedAdjustments has removed
in favour of Rails.application.config.spree.calculators.

The classes affected are:
Spree::ShippingMethod
Spree::TaxRate
Spree::Promotion::Actions::CreateAdjustment
Spree::Promotion::Actions::CreateItemAdjustment

core/app/models/concerns/spree/calculated_adjustments.rb

@@ -10,24 +10,6 @@ module CalculatedAdjustments
       validates :calculator, presence: true
     end
 
-    class_methods do
-      def calculators
-        Spree::Deprecation.warn("Calling .calculators is deprecated. Please access through Rails.application.config.spree.calculators")
-
-        spree_calculators.send model_name_without_spree_namespace
-      end
-
-      private
-
-      def model_name_without_spree_namespace
-        to_s.tableize.tr('/', '_').sub('spree_', '')
-      end
-
-      def spree_calculators
-        Spree::Config.environment.calculators
-      end
-    end
-
     def calculator_type
       calculator.class.to_s if calculator
     end