Remove unused Product#on_demand

app/models/concerns/product_stock.rb

@@ -5,13 +5,6 @@ require 'active_support/concern'
 module ProductStock
   extend ActiveSupport::Concern
 
-  def on_demand
-    raise 'Cannot determine product on_demand value of product with multiple variants' if
-      variants.size > 1
-
-    variants.first.on_demand
-  end
-
   def on_hand
     variants.map(&:on_hand).reduce(:+)
   end

spec/models/concerns/product_stock_spec.rb

@@ -6,12 +6,6 @@ RSpec.describe ProductStock do
   let(:product) { create(:simple_product) }
 
   context "when product has one variant" do
-    describe "product.on_demand" do
-      it "is the products first variant on_demand" do
-        expect(product.on_demand).to eq(product.variants.first.on_demand)
-      end
-    end
-
     describe "product.on_hand" do
       it "is the products first variant on_hand" do
         expect(product.on_hand).to eq(product.variants.first.on_hand)
@@ -24,13 +18,6 @@ RSpec.describe ProductStock do
       product.variants << create(:variant, product:)
     end
 
-    describe "product.on_demand" do
-      it "raises error" do
-        expect { product.on_demand }
-          .to raise_error(StandardError, /Cannot determine product on_demand value/)
-      end
-    end
-
     describe "product.on_hand" do
       it "is the sum of the products variants on_hand values" do
         expect(product.on_hand)