Remove deprecated Spree::DefaultPrice#find_or_build_default_price

Please, use #default_price_or_build instead.

Ref solidusio#4960

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

@@ -23,12 +23,6 @@ def default_price_or_build
         prices.build(self.class.default_price_attributes)
     end
 
-    # @deprecated Use {#default_price_or_build} instead.
-    def find_or_build_default_price
-      default_price_or_build
-    end
-    deprecate find_or_build_default_price: :default_price_or_build, deprecator: Spree::Deprecation
-
     # Select from {#prices} the one to be considered as the default
     #
     # This method works with the in-memory association, so non-persisted prices

core/spec/models/spree/variant_spec.rb

@@ -334,25 +334,6 @@
     end
   end
 
-  describe '#find_or_build_default_price' do
-    it 'is deprecated' do
-      without_partial_double_verification do
-        expect(Spree::Deprecation).to receive(:warn)
-      end
-      variant.find_or_build_default_price
-    end
-
-    it 'is an alias for #default_price_or_build' do
-      without_partial_double_verification do
-        allow(Spree::Deprecation).to receive(:warn)
-      end
-
-      expect(variant).to receive(:default_price_or_build)
-
-      variant.find_or_build_default_price
-    end
-  end
-
   describe '#has_default_price?' do
     context 'when default price is present and not discarded' do
       it 'returns true' do