Fixes rubocop offense inverse_of on payment model

- some clean up unused method too

.rubocop_todo.yml

@@ -474,13 +474,12 @@ RSpecRails/InferredSpecType:
     - 'spec/requests/voucher_adjustments_spec.rb'
     - 'spec/routing/stripe_spec.rb'
 
-# Offense count: 2
+# Offense count: 1
 # Configuration parameters: IgnoreScopes, Include.
 # Include: app/models/**/*.rb
 Rails/InverseOf:
   Exclude:
     - 'app/models/spree/order.rb'
-    - 'app/models/spree/payment.rb'
 
 # Offense count: 35
 # Configuration parameters: Include.

app/models/spree/payment.rb

@@ -22,6 +22,7 @@ module Spree
 
     has_many :offsets, -> { where("source_type = 'Spree::Payment' AND amount < 0").completed },
              class_name: "Spree::Payment", foreign_key: :source_id,
+             inverse_of: :source,
              dependent: :restrict_with_exception
     has_many :log_entries, as: :source, dependent: :destroy
 
@@ -115,10 +116,6 @@ module Spree
       amount - offsets_total
     end
 
-    def can_credit?
-      credit_allowed.positive?
-    end
-
     def build_source
       return if source_attributes.nil?
       return unless payment_method&.payment_source_class

spec/models/spree/payment_spec.rb

@@ -607,19 +607,6 @@ RSpec.describe Spree::Payment do
       end
     end
 
-    context "#can_credit?" do
-      it "is true if credit_allowed > 0" do
-        payment = build_stubbed(:payment)
-        allow(payment).to receive(:credit_allowed) { 100 }
-        expect(payment.can_credit?).to be true
-      end
-      it "is false if credit_allowed is 0" do
-        payment = build_stubbed(:payment)
-        allow(payment).to receive(:credit_allowed) { 0 }
-        expect(payment.can_credit?).to be false
-      end
-    end
-
     context "#save" do
       context "completed payments" do
         it "updates order payment total" do