Remove deprecated Spree::DefaultPrice#currently_valid_prices

Please, use Spree::Variant#default_price instead.

Ref solidusio#4639.

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

@@ -14,15 +14,6 @@ def self.default_price_attributes
       end
     end
 
-    # Returns `#prices` prioritized for being considered as default price
-    #
-    # @deprecated
-    # @return [ActiveRecord::Relation<Spree::Price>]
-    def currently_valid_prices
-      prices.currently_valid
-    end
-    deprecate :currently_valid_prices, deprecator: Spree::Deprecation
-
     # Returns {#default_price} or builds it from {Spree::Variant.default_price_attributes}
     #
     # @return [Spree::Price, nil]

core/spec/models/spree/variant_spec.rb

@@ -373,26 +373,6 @@
     end
   end
 
-  describe '#currently_valid_prices' do
-    around do |example|
-      Spree::Deprecation.silence do
-        example.run
-      end
-    end
-
-    it 'returns prioritized prices' do
-      price_1 = create(:price, country: create(:country))
-      price_2 = create(:price, country: nil)
-      variant = create(:variant, prices: [price_1, price_2])
-
-      result = variant.currently_valid_prices
-
-      expect(
-        result.index(price_1) < result.index(price_2)
-      ).to be(true)
-    end
-  end
-
   context "#cost_currency" do
     context "when cost currency is nil" do
       before { variant.cost_currency = nil }