Update mailer subscriber for Solidus 4 compatibility

- Update method name from order_finalized to send_confirmation_email
- Change target class from Spree::MailerSubscriber to Spree::OrderMailerSubscriber
- Remove version conditional since gem now only supports Solidus 4+

Author: kjriga

app/decorators/subscribers/solidus_tracking/spree/mailer_subscriber/disable_confirm_email.rb

@@ -6,12 +6,12 @@ module MailerSubscriber
       module DisableConfirmEmail
         def self.prepended(base)
           base.module_eval do
-            alias_method :original_order_finalized, :order_finalized
+            alias_method :original_send_confirmation_email, :send_confirmation_email
 
-            def order_finalized(event)
+            def send_confirmation_email(event)
               return if SolidusTracking.configuration.disable_builtin_emails
 
-              original_order_finalized(event)
+              original_send_confirmation_email(event)
             end
           end
         end
@@ -20,6 +20,4 @@ def order_finalized(event)
   end
 end
 
-if Spree.solidus_gem_version >= Gem::Version.new('2.9.0')
-  Spree::MailerSubscriber.prepend(SolidusTracking::Spree::MailerSubscriber::DisableConfirmEmail)
-end
+Spree::OrderMailerSubscriber.prepend(SolidusTracking::Spree::MailerSubscriber::DisableConfirmEmail)