Remove Benefit#level

This just adds to the complexity of the benefit interface, and does not
provide anything to the codebase. Let's remove before it starts being
used.

Author: mamhoff

promotions/app/models/concerns/solidus_promotions/benefits/line_item_benefit.rb

@@ -6,10 +6,6 @@ module LineItemBenefit
       def can_discount?(object)
         object.is_a? Spree::LineItem
       end
-
-      def level
-        :line_item
-      end
     end
   end
 end

promotions/app/models/concerns/solidus_promotions/benefits/order_benefit.rb

@@ -6,10 +6,6 @@ module OrderBenefit
       def can_discount?(_)
         false
       end
-
-      def level
-        :order
-      end
     end
   end
 end

promotions/app/models/concerns/solidus_promotions/benefits/shipment_benefit.rb

@@ -6,10 +6,6 @@ module ShipmentBenefit
       def can_discount?(object)
         object.is_a?(Spree::Shipment) || object.is_a?(Spree::ShippingRate)
       end
-
-      def level
-        :shipment
-      end
     end
   end
 end

promotions/app/models/solidus_promotions/benefit.rb

@@ -75,11 +75,6 @@ def to_partial_path
       "solidus_promotions/admin/benefit_fields/#{model_name.element}"
     end
 
-    def level
-      raise NotImplementedError, "Please implement the correct interface, or include one of the `SolidusPromotions::Benefits::OrderBenefit`, " \
-        "`SolidusPromotions::Benefits::LineItemBenefit` or `SolidusPromotions::Benefits::ShipmentBenefit` modules"
-    end
-
     def available_conditions
       possible_conditions - conditions.select(&:persisted?)
     end

promotions/spec/models/solidus_promotions/benefit_spec.rb

@@ -139,12 +139,4 @@ def compute_line_item(_line_item, _options) = 1
       expect(subject).to be_nil
     end
   end
-
-  describe "#level" do
-    subject { described_class.new.level }
-
-    it "raises an error" do
-      expect { subject }.to raise_exception(NotImplementedError)
-    end
-  end
 end

promotions/spec/models/solidus_promotions/benefits/adjust_line_item_spec.rb

@@ -16,10 +16,4 @@
 
     it { is_expected.to eq("solidus_promotions/admin/benefit_fields/adjust_line_item") }
   end
-
-  describe "#level" do
-    subject { described_class.new.level }
-
-    it { is_expected.to eq(:line_item) }
-  end
 end

promotions/spec/models/solidus_promotions/benefits/adjust_shipment_spec.rb

@@ -32,10 +32,4 @@
       it { is_expected.to be true }
     end
   end
-
-  describe "#level" do
-    subject { described_class.new.level }
-
-    it { is_expected.to eq(:shipment) }
-  end
 end