Remove unused StockLocation#backorderable?

app/models/spree/stock_location.rb

@@ -35,9 +35,5 @@ module Spree
     def count_on_hand(variant)
       stock_item(variant).try(:count_on_hand)
     end
-
-    def backorderable?(variant)
-      stock_item(variant).try(:backorderable?)
-    end
   end
 end

spec/models/spree/stock_location_spec.rb

@@ -30,9 +30,5 @@ module Spree
     it 'finds a count_on_hand for a variant' do
       expect(subject.count_on_hand(variant)).to eq 15
     end
-
-    it 'finds determines if you a variant is backorderable' do
-      expect(subject.backorderable?(variant)).to eq false
-    end
   end
 end